How to Prevent the Coal Roller Screen Shaft From Bending or Breaking

Introduction

Roller screen is also called wobbler feeder and disc screen. In the coal processing system, the roller screen is widely used due to its efficient and reliable screening performance. However, under the long-term and continuous high-load operation conditions, the roller screen is prone to some failures, such as the bending or fracture of the screen shaft, which forces the production to be interrupted. This not only affects the production efficiency but also increases the maintenance costs and safety risks. In order to find effective strategies to prevent the bending of the screen shaft of the coal roller screen, understanding the underlying fundamental reasons and taking forward-looking preventive measures are the key to improving the equipment reliability and optimizing the production efficiency.

The function of the roller screen shaft

Sieving function

Achieve material classification: When the materials are spread on the sieve surface, the particles smaller than the sieve aperture size will fall through the aperture under the action of gravity and the stirring of the roller screen disc, becoming the sieve residue.

Control classification accuracy: The gap size between the roller screen shafts directly determines the final particle size of the product in the roller screen screening operation. The processing and installation accuracy of the roller screen shaft ensures the consistency and accuracy of the gap.

Conveying and Propulsion

Providing forward power: The rotating screen disc of the roller screen continuously conveys the material from the feed end to the discharge end through the frictional force with the material.

Controlling processing speed: The rotational speed of the screen shaft directly determines the residence time of the material on the screen surface. A faster rotation speed leads to faster conveying and higher processing capacity but may result in insufficient screening; a slower rotation speed leads to more thorough screening but a decrease in processing capacity.

Prevention and self-cleaning

Dynamic clearance cleaning: During the rotation of the screen disc, its contour constantly changes and alters the relative position with the adjacent screen discs. This dynamic change effectively prevents fibrous, sheet-like, and other easily clogging materials from getting stuck in the gaps.

Compulsory discharge: Even if there are difficult-to-crush flexible debris (such as plastic films, wood chips) wrapped around the screen shaft of the roller screen, the rotating motion of the screen disc can forcibly transport them towards the discharge end and eventually discharge them, rather than blocking on the screen surface.

Reasons for bending or fracture of roller screen’s sieve shaft

Operation and maintenance factors

Overload operation

Excessive or uneven feeding: Instantaneous or long-term exceeding the designed processing capacity, the impact and torque borne by the sieve shaft far exceed the design value.

Change in material properties: If the particle size of the coal fed into the screen becomes larger, the hardness increases (for example, mixed with gangue, debris), or the moisture content is too high resulting in increased stickiness and difficulty in screening, the load on the sieve shaft of the roller screen will increase sharply.

Foreign objects entrapment and impact

This is the most direct and violent cause leading to the deformation and fracture of the screen shaft. Hard foreign objects such as ironware, wood blocks, and large pieces of gangue mixed in the coal are prone to getting stuck between the screen plates or between the screen shaft and the side walls.

When the foreign objects get stuck, the drive motor is still running, and the huge torque will directly act on the screen shaft of the roller screen. In mild cases, it will cause the screen shaft to twist and deform; in severe cases, it will break on the spot. At the same time, the direct impact of large pieces of material on the screen shaft will also cause bending.

Poor lubrication

If the lubrication of the bearing housing is not timely or the wrong lubricating grease is used, it will cause damage to the bearings and result in the bearings getting stuck.

Once the bearing gets stuck, the corresponding sieve shaft will be fixed in place, while the other sieve shafts are still rotating. This is highly likely to cause the shaft to be broken or damage to the related transmission components.

Factors of equipment aging and wear

Severe wear of the screen plate

After long-term use, due to continuous friction and impact, the surface material of the screen plate gradually wears away, causing the mesh gaps on the screen plate to gradually increase. This not only affects the accuracy of screening but also allows larger material particles to enter the subsequent screen shaft and equipment. The wear of the screen plate is uneven, which leads to uneven force distribution on the screen shaft during operation. The imbalance of force will affect the stable operation of the rotary screen and may cause vibration, noise and other problems, and even result in serious faults such as screen shaft fracture.

Bearings and bearing housings wear out

After the roller screen has been running continuously for a long time, the gap between the bearings and the bearing housings gradually increases. Due to the existence of this gap, the rotating part of the screen shaft will generate vibrations during operation. These vibrations will intensify over time and pose a threat to the overall stability of the roller screen. They will also cause mechanical stress on the screen shaft itself, thereby leading to deformation of the screen shaft.

Measures for preventing coal roller screen shaft bending or fracture

Reasonably control the feeding volume

By installing measuring devices or setting feeding alarm systems, ensure that the feeding volume is always within the designed processing capacity, avoiding instantaneous overload or long-term overloading. At the same time, optimize the feeding method to ensure the uniform distribution of materials, reducing local impact.

Strengthen material pre-treatment

Before the coal enters the roller screen, set up pre-sieving or impurity removal devices to effectively remove large pieces of shale, iron objects, wooden blocks, etc., which are hard foreign objects, reducing the risk of foreign object clogging and impact. For coal with excessive moisture, it can be dried to reduce stickiness and improve screening efficiency.

Regular lubrication and maintenance

Develop a detailed lubrication plan, regularly lubricate the bearing housing, ensure the use of the correct lubricant, and regularly check the lubrication status. At the same time, establish a device maintenance file to record the time, content, and replaced components of each maintenance, so as to promptly detect and handle potential problems.

Select high-strength materials

When manufacturing the shafts of the roller screen, higher-strength materials such as alloy steel can be chosen to enhance the bearing capacity and fatigue resistance of the shafts. At the same time, optimize the structural design of the shafts to reduce stress concentration points and lower the risk of fracture.

Improve the design of the screen plates

To address the issue of severe wear of the screen plates, the design of the screen plates can be improved, such as using more wear-resistant materials, optimizing the shape and size of the screen gaps, etc., to extend the service life of the screen plates and reduce the uneven force on the shafts caused by the wear of the screen plates.

Install vibration monitoring and protection systems

An overload protection device can be set up. When the torque borne by the shaft exceeds the design value, the power supply should be automatically cut off or the rotational speed should be reduced to protect the shafts from damage.

Conclusion

The bending and fracture of the rollers in the coal roller screen are not caused by a single factor, but are the result of the combined effects of equipment design, daily operation, maintenance, and material management.