Roller Screen in the design of the crushing and screening station
Introduction
Crushing and screening is an indispensable core process in the field of mineral processing. Efficiency and reliability directly determine the production capacity, product quality and economic benefits of the entire production line. The physical properties of the materials to be processed are becoming increasingly complex, especially high moisture, high viscosity (such as wet sticky coal, sandy ores), easily tangled materials, and large-sized irregular materials. Traditional screening equipment represented by vibrating screens often have limitations when dealing with such complex conditions. Roller Screen avoids the traditional vibrating screen’s idea of relying on material vibration for stratification and screening, and can effectively cope with the above-mentioned complex situations.
Core structure composition of Roller Screen
Screen Box and Frame
The screen box is the overall framework of the Roller Screen, enclosing all the screen shafts, bearings and transmission devices, forming a closed or semi-closed working space.
The screen box needs to have sufficient rigidity and strength to support all the screen shafts and the material loads they bear, ensuring that the screen shafts maintain precise parallelism and spacing during long-term operation.
To prevent dust from spilling out and meet environmental protection requirements, Roller Screen mostly adopts a fully sealed structural design. At the position where the screen shafts pass through the side plate of the box, a vane-type seal or other efficient sealing components will be used to ensure the reliability of the dynamic seal.
Screen Shafts and Screen Discs/Plates
Shaft
The quantity is determined by the effective area of the screen surface and the processing capacity requirement. The screen shaft needs to undergo precise machining and heat treatment to ensure its straightness and bending and torsion resistance strength.
Disc/Plate
The common shapes of sieve plates include parabolic, elliptical, lily-petal, and gear-shaped ones. The parabolic and elliptical shapes can provide the materials with stronger throwing and sinusoidal wave motion trajectories, which is beneficial for loosening the materials; while the gear-shaped ones focus on the forced flipping of large pieces of materials and the shearing of viscous materials.
Drive System
Interconnected Drive
Using a high-power motor, through a reducer and chains, gears, etc., all the sieve shafts are driven simultaneously. This method has a relatively simple structure and lower cost, but the drawback is that if one sieve shaft gets stuck or fails, it may cause the entire system to stop, and it is difficult to implement differentiated speed control for each sieve shaft.
Independent Drive
Each sieve shaft or each group of sieve shafts is driven by an independent “motor + reducer” unit. The overall layout is more flexible, and the rotational speed of the corresponding sieve shafts can be adjusted separately according to different screening requirements to achieve differentiated screening parameter control. However, this drive method requires multiple sets of drive units, resulting in higher overall equipment costs, and the wiring and control system design are relatively more complex.
Connecting component
The motor is usually connected to the reducer and the reducer is connected to the screen shaft through a coupling. To prevent damage to the motor or the reducer due to overload, couplings with safety protection functions are often used, such as elastic pin couplings or hydraulic couplings. When the torque exceeds the set value, the pin is cut or the hydraulic coupling slips, thereby cutting off the power transmission and protecting the key components.
Scrapers/Cleaning Blades
Below the screening shaft, fixed scrapers or comb-like cleaning devices can be installed. The tips of these devices extend between adjacent screen sheets. When the screening shaft rotates, they can remove the materials adhering to the roots or sides of the screen sheets, ensuring that the screen remains unobstructed at all times. Regular inspection and cleaning of these blades are an important part of maintenance work.
Determination of Key Design Parameters for Roller Screen
Design of Dimensional Parameters
Screen surface width (B)
The screen surface width should be designed to ensure that the largest-sized materials can pass through smoothly without causing “bridging” blockage. The empirical design guideline requires that the effective width B of the screen surface should be no less than 3 times the maximum feed particle size Dmax.
Screen surface length (L)
The length of the screen surface determines the time that materials spend on the screen, thereby affecting the screening efficiency. The longer the length, the more opportunities the materials have to be fully screened, and the higher the screening efficiency. However, the equipment size and cost also increase accordingly. Generally, the screen surface length L is usually 3 to 8 times the screen surface width B.
Design of Geometric and Kinematic Parameters
Screen Surface Angle
The inclination angle mainly affects the conveying speed of the materials. The greater the inclination angle, the greater the component force that makes the materials slide forward along the sieve surface, the faster the movement speed, and the processing capacity will increase accordingly. However, the residence time will be shortened, which may reduce the screening efficiency; conversely, the smaller the inclination angle, the slower the speed, the more thorough the screening will be, but the processing capacity will decrease.
Shaft Speed
The rotational speed determines the intensity and frequency of the screening action of the screen plate on the material. If the rotational speed is too low, it will not be able to effectively loosen the material, especially for viscous materials. On the other hand, if the rotational speed is too high, the material may be lifted excessively and even go beyond the screen axis, resulting in “material leakage” and a decrease in screening efficiency. At the same time, it will also increase energy consumption and wear.
Design of Screening Parameters
Screen Aperture/Gap Size
The sieve aperture size is determined by the center distance between adjacent sieve shafts and the thickness of the sieve plate. During the design process, this size needs to be determined according to the required screening particle size specified by the process.
Disc Shape and Arrangement
Different screen shapes exert different force patterns on the materials, and the choice of shape depends on the main characteristics of the materials. For viscous materials that require strong loosening and tumbling, parabolic or lily-shaped screen sheets with a larger eccentricity are more effective. The arrangement of screen sheets on the shaft, especially the phase difference (offset angle) between adjacent screen shafts, is crucial for achieving self-cleaning functionality and must be precisely designed and installed.
Roller Screen in the process layout of the crushing and screening station
Process flow
Under the premise of meeting process requirements and having sufficient maintenance space, the equipment layout should be as compact as possible to save valuable land resources. Especially in areas with limited space or complex terrain, the vertical space should be fully utilized and a multi-layer layout scheme should be adopted. By taking advantage of the favorable natural terrain slope, the amount of earthwork and the height of material lifting can be reduced, thereby lowering construction and operation costs.
Sufficient space must be reserved for daily inspections, lubrication, spare parts replacement, and the hoisting and maintenance of large components (such as motors, reducers, screen shafts). The design of maintenance passages, stairs, and platforms should comply with safety regulations.
All moving parts must be equipped with reliable protective covers. At the connection points of the equipment, especially at the material transfer points, effective sealing and dust removal measures must be taken to control dust pollution. At the same time, the layout of fire protection, lighting, and emergency stop systems should be considered.
Integration with upstream and downstream equipment
The position of Roller Screen in the process chain determines the complexity of its interface design. A typical process is: “Feed conveyor → Roller Screen → (material on the screen) → Crusher → (material below the screen) → Product conveyor”.
Upstream feed connection
It is essential to avoid concentrating the materials on one side or in the middle of the screen surface, as this will cause local overload and increased wear on the screen surface, resulting in low screening efficiency. Therefore, an effective material distribution device should be set up before the feed inlet of the Roller Screen. The ideal solution is to equip a plate feeder or a vibrating feeder. If there is no independent feeder, at least the chute at the head of the upstream belt conveyor should be carefully designed to disperse the columnar flow of the materials through guide plates, diversion cones, etc., and distribute them evenly across the entire width of the screen surface.
At the feed inlet of the Roller Screen, there is usually a chute or a buffer hopper. The design of the chute should ensure that the materials slide smoothly into the screen surface at an appropriate angle and speed, avoiding excessive impact force that could damage the screen sheet. The wear-resistant lining of the chute is indispensable.
Conclusion
The Roller Screen demonstrates significant technical advantages over traditional screening equipment when dealing with wet, sticky, large, and mixed materials. Its successful application in crushing and screening stations relies on a systematic and comprehensive scientific methodology that runs through the entire process of design, selection, layout, installation, and operation.
