Vibrating screen is an important sorting and grading equipment in the production of modified plastics. Its working principle is to drive the incoming materials to stratify and pass through screen holes by the vibration of the screen body, so as to achieve the purpose of material sorting and grading.
During my visits to compounding factories, I found an interesting phenomenon. In one factory, after the pelletized finished products passed through the vibrating screen, the reject rate was twice as high as the qualified rate. After careful inspection, it turned out that one corner of the vibrating screen was leaning against the pelletizer. The mutual vibration affected both pelletizing and screening processes and caused abnormalities. Later, the vibrating screen was separated from the pelletizer, and the screening work returned to normal. However, material waste had already been caused, which was quite a pity.
Therefore, discovering faults and solving problems in a timely manner to ensure the stable operation of vibrating screens is not only conducive to improving production efficiency, but also of great significance to sorting operations.
As a common piece of equipment in modified plastics factories, vibrating screens are subject to a variety of common faults, which are mainly caused by mechanical, electrical and human factors. Common faults of vibrating screens include poor screening quality, failure to meet operational technical indicators, and severe wear or damage of components. To reduce failures of vibrating screens and avoid affecting the quality of finished pellets, we have sorted out relevant solutions for you.
Many factors affect the screening effect, including feed material properties, equipment factors and operational factors. The main causes of poor screening quality are blocked screen holes, severely worn screen holes, uneven feeding and over-thick material layer on the screen surface.
Poor Screening Quality
1. Blocked Screen Holes
When the incoming materials have high mud content and water content, the materials will stick to the screen holes and cause blockage. In this case, clean the screen holes first, and then properly adjust the water spray volume and the inclination angle of the screen surface.
2. Severely Worn Screen Holes
Long-term use of the screen mesh will lead to severe wear of screen holes, which will seriously affect the screening effect. Repair the worn screen holes, and replace the screen mesh if the wear is too severe.
3. Uneven Feeding
An excessively narrow feeding trough will prevent materials from distributing evenly over the entire screen surface, resulting in underutilization of the screen surface and poor screening effect. Adjust the width of the feeding trough to realize even feeding.
4. Over-thick Material Layer on the Screen Surface
Excessively thick material layer may be caused by increased feeding volume, blocked screen holes or small inclination angle of the screen surface. Make adjustments according to specific situations.
The operational technical indicators of vibrating screens include rotating speed, exciting force, amplitude and frequency. Common faults include failure to start or excessively small amplitude, insufficient rotating speed, weak exciting force and inconsistent amplitude at four measuring points.
Failure to Meet Operational Technical Indicators
1. Failure to Start or Excessively Small Amplitude
When the vibrating screen cannot start or the amplitude is too small, first check for electrical faults such as damaged motor and insufficient voltage. If no electrical problems are found, check mechanical parts. Clear material accumulation on the screen surface if any; fasten loose coupling bolts on the vibrator and replace caked grease in a timely manner.
2. Insufficient Rotating Speed
Insufficient rotating speed may result from electrical faults, which shall be troubleshooted and handled in time. It may also be caused by loose transmission belts, so tension the transmission belts properly.
3. Weak Exciting Force
Weak exciting force is usually caused by incorrect installation or insufficient weight of counterweights on the flywheel. Adjust the counterweights on the flywheel accordingly.
4. Inconsistent Amplitude at Four Measuring Points
Inconsistent amplitude at four points is generally caused by unsynchronized operation of two vibrators on the same axis or material segregation. Adjust the two vibrators to keep synchronous operation and eliminate material segregation in a timely manner.
After long-term operation, some components of the vibrating screen will suffer severe wear or even fracture. Common faults include fractured pipe beams, fractured cross beams and fractured screen frames.
Severe Wear and Damage of Components
1. Fractured Pipe Beams
Thin pipe beam walls may lead to fracture. Replace with thick-walled pipes of the same model or pipe beams of a larger model. However, avoid using overly thick or oversized pipes, as they will increase the vibrating mass of the screen and trigger other problems. For dewatering and medium removal screens, horizontal and vertical pressure strips shall be installed at all connections of screen plates. Without vertical pressure strips, water will leak through gaps between screen meshes and scour pipe beams, causing fracture at the scoured areas. In addition, wider screens are more likely to have fractured pipe beams. Based on practical experience, dual-channel structure is recommended for screens with a width over 3 meters.
2. Fractured Cross Beams
Fractured cross beams are mainly caused by long-time operation under critical frequency, loose high-strength bolts for fastening side plates, severely deformed springs leading to large height difference between left and right sides, or excessive weight deviation of eccentric blocks. All these problems will damage structural parts and break cross beams. Replace damaged structural parts and cross beams, fasten loose bolts and adjust the weight of eccentric blocks.
3. Fractured Screen Frames
Screen frames are prone to fracture due to vibration and shaking. The optimal solution is to thicken the side plates, or install additional reinforcing plates on local areas of side plates near vibrators to enhance the overall rigidity of the screen frame.
Abnormal Operating Noise
Abnormal noise during operation may be caused by damaged springs, worn bearings, loose bearing fixing bolts or untensioned screen meshes.
1. Damaged Springs
Damaged springs will generate loud noise. Replace damaged springs immediately to prevent production accidents.
2. Worn Bearings
Severely worn bearings will cause abnormal loud noise. Stop the machine and replace the bearings in a timely manner.
3. Loose Bearing Fixing Bolts
Loose bolts for fixing bearings will lead to abnormal operating noise. Fasten the bolts right away.
4. Untensioned Screen Mesh
Untensioned screen mesh not only causes abnormal noise, but also affects screening effect. Tighten the screen mesh promptly.
Daily Maintenance Notes for Vibrating Screens
- Optimize equipment design and guarantee manufacturing precision. Select a suitable vibrating screen according to actual service conditions and application purposes, and leave a proper margin in model selection.
- Complete preparation work before installation, and follow relevant specifications and steps in accordance with installation drawings.
- Operate in compliance with relevant rules. Make full pre-start preparations and strictly follow the startup and shutdown sequence.
- Conduct regular inspection and maintenance during operation. Perform maintenance work as required, pay close attention to vulnerable parts, and troubleshoot problems once found.