Introduction: The Importance of Screw Conveyors in Modern Industrial Production
Screw conveyors, a type of continuous conveying equipment, are widely used in industrial sectors such as grain processing, chemical production, building materials manufacturing, and mineral processing. Their simple structure, good sealing performance, and ease of operation and maintenance make them indispensable components in modern production lines. However, during operation, screw conveyors often experience failures due to material characteristics, operating conditions, equipment wear, and other factors, which directly affect production efficiency and equipment lifespan.
This article systematically analyzes common types of failures in screw conveyor operation, delves into their causes from perspectives including mechanical structure, electrical systems, and operation and maintenance, and proposes targeted solutions and preventive measures. Through scientific fault diagnosis methods and standardized maintenance strategies, the operational reliability of screw conveyors can be significantly improved, equipment service life extended, and continuous stable operation of production lines ensured.
1. Working Principle and Structural Composition of Screw Conveyors
1.1 Basic Working Principle
A screw conveyor uses rotating helical blades to push material along a fixed trough, enabling horizontal, inclined, or vertical conveying. When the screw shaft rotates, the material, under its own weight and friction with the trough wall, does not rotate with the helical blades but instead moves forward along the trough, similar to a non-rotating nut translating along a screw.
The conveying capacity of a screw conveyor depends on the screw diameter, pitch, rotational speed, and material characteristics. Typically, the conveying capacity Q can be calculated by the formula: Q = 47D²φρSnψ, where D is the screw diameter (m), φ is the filling coefficient, ρ is the material bulk density (t/m³), S is the pitch (m), n is the rotational speed (r/min), and ψ is the inclined conveying coefficient. Understanding this basic relationship is crucial for fault diagnosis.
1.2 Main Structural Components
A screw conveyor mainly consists of the following components: drive unit (including motor, reducer, coupling, etc.), screw shaft and blades (core working parts), trough and cover plates (forming the enclosed conveying space), bearing assemblies (supporting the screw shaft, including head bearings, intermediate bearings, and tail bearings).
2. Analysis and Solution for Decreased Conveying Capacity
2.1 Fault Phenomena and Cause Analysis
Common Fault Phenomena: Conveying volume is significantly lower than the design value or initial operating value; material accumulates at the feed inlet and cannot be conveyed promptly; motor current abnormally increases or fluctuates; material discharge at the outlet is uneven or intermittent.
Cause Analysis:
- Changes in Material Characteristics: Increased material moisture leads to enhanced adhesion and poor flowability; material particle size is uneven or contains large impurities; material bulk density changes beyond the design range.
- Equipment Wear and Blockage: Wear of helical blades reduces pushing efficiency; material adhesion on the inner wall of the trough forms scaling, reducing the effective flow area; bearing damage increases rotational resistance.
- Improper Operating Parameters: Feed volume is too large, exceeding equipment capacity; rotational speed setting is unreasonable; operating parameters are not adjusted correspondingly with changes in inclination angle.
2.2 Solutions and Preventive Measures
Material Pre-treatment: Control material moisture content within a reasonable range (generally ≤15%); install screening devices to remove large impurities; for easily adhering materials, install anti-adhesion lining plates on the inner wall of the trough.
Equipment Modification and Maintenance: Use wear-resistant materials for helical blades (such as 65Mn steel, wear-resistant alloys); regularly clean scaling on the inner wall of the trough, recommended inspection and cleaning every 200 hours of operation; optimize the clearance between blades and trough, maintaining a reasonable range (typically 5-10mm).
Operation Optimization: Adjust feed speed according to material characteristics to avoid overload; optimize rotational speed setting, generally controlled within the range of 20-60 r/min; regularly check motor current and establish a current-load correspondence table.
3. Analysis of Abnormal Vibration and Noise Faults
3.1 Vibration Source Identification and Diagnosis
Vibration Characteristics and Possible Causes:
- Low-frequency periodic vibration: Screw shaft bending, dynamic balance failure
- High-frequency continuous vibration: Bearing damage, blade contact with the trough
- Impact-type irregular vibration: Metal foreign objects in the material, loose connection bolts
- Axial movement vibration: Thrust bearing wear, axial positioning failure
3.2 Vibration and Noise Reduction Solutions
Systematic Solutions:
Dynamic Balance Correction: Dynamic balance testing should be performed after screw shaft assembly, with balance accuracy not lower than G6.3 grade; check dynamic balance status every 6 months during use.
Bearing Optimization: Select precision bearings with low vibration (e.g., SKF or NSK); use labyrinth seals to prevent dust ingress; regularly apply high-quality lubricating grease.
Structural Reinforcement: Increase the number of intermediate support bearings to shorten the span; strengthen the connection stiffness between the trough and the support frame; install elastic couplings at the drive end to absorb vibration.
Install Vibration Isolation Devices: Install rubber vibration dampers or spring shock absorbers on the equipment base; use flexible installation for the drive motor.
4. Bearing and Seal System Failures
4.1 Analysis of Bearing Failure Modes
Common Bearing Failure Manifestations: Abnormal temperature rise (bearing temperature exceeds ambient temperature +45°C or absolute temperature exceeds 75°C); increased noise (continuous or intermittent abnormal sounds during operation); aggravated vibration (radial and axial vibration values continuously increase); rotation sticking (feeling uneven resistance during manual turning).
In-depth Analysis of Failure Causes:
- Poor Lubrication: Improper selection of lubricating grease (viscosity too high or too low); insufficient or excessive filling; lubricant contamination (mixed with dust, moisture).
- Improper Installation: Improper fit between bearing and shaft journal (too tight or too loose); uneven force during installation, causing raceway damage; improper installation of seals.
- Abnormal Load: Screw shaft bending causing additional radial force; material blockage leading to increased axial force; coupling misalignment.
4.2 Seal System Failure and Improvement
Seal failure in screw conveyors is a main cause of bearing damage and environmental pollution. Traditional packing seals are prone to wear and leakage, while mechanical seals require high installation precision and are costly.
Seal System Optimization Solutions:
Combined Seals: Adopt a triple-seal structure of “labyrinth seal + skeleton oil seal + packing seal” to adapt to different working condition requirements.
Application of New Materials: Use temperature-resistant and wear-resistant materials such as fluororubber and PTFE for seals; add wear-resistant coatings to reduce shaft journal wear.
Structural Improvements: Design adjustable seal glands for easy wear compensation; add pressure relief grooves to prevent pressure buildup.
Cleaning System: Add air seals outside the seal cavity to introduce clean compressed air and prevent dust ingress.
5. Motor and Drive System Failures
5.1 Analysis of Motor Overload Faults
Statistics: 65% of motor failures are caused by overload, of which 40% are due to material blockage, 25% due to bearing damage, and 30% due to improper installation.
Motor Overload Protection Strategies:
- Proper Selection: Motor power should have an appropriate margin, generally selected at 1.1-1.3 times the calculated power; use Y-series or YE3 series high-efficiency motors.
- Comprehensive Protection: Install electronic overload relays, setting reasonable trip current (usually 1.05-1.2 times the rated current); add stall protection and phase failure protection.
- Load Monitoring: Install current monitoring instruments to display operating current in real time; set upper and lower current limit alarms to provide early warning of abnormal conditions.
5.2 Common Reducer Failures and Maintenance
Reducer Failure Signs: Abnormal noise (metal impact sounds, periodic knocking sounds); abnormal oil temperature rise (exceeding ambient temperature +40°C); lubricant leakage or contamination (milky white, containing metal particles); output shaft vibration or axial movement.
Reducer Maintenance Key Points:
Oil Management: Replace lubricating oil after the first 300 hours of operation, then every 6 months or 3000 hours; use the designated gear oil grade (e.g., ISO VG 220).
Installation Precision: Alignment deviation between reducer, motor, and working machine ≤0.1mm; use laser alignment tools to improve installation accuracy.
Regular Inspection: Check oil level and quality monthly; check fastener bolts quarterly; conduct an annual gear-wear inspection with the casing open.
Temperature Control: Install cooling fans when ambient temperature exceeds 35°C; add oil coolers when oil temperature exceeds 85°C.
6. Preventive Maintenance and Fault Management System
6.1 Establishing a Preventive Maintenance System
A preventive maintenance system should include the following four levels:
- Daily Inspection: Operators check equipment operating status each shift, recording parameters such as current, temperature, and noise.
- Regular Maintenance: Maintenance personnel perform basic tasks such as lubrication, tightening, and cleaning in accordance with the schedule.
- Professional Testing: Conduct monthly vibration analysis and infrared thermography to detect potential faults early.
- Overhaul Management: Perform systematic disassembly and inspection annually or every 5000 hours of operation, replacing worn parts.
6.2 Application of Fault Diagnosis Technologies
Vibration Analysis: Applied to bearing, gear, and unbalance fault diagnosis, offering early warning and accurate localization. Requires establishing baseline spectra and regular comparison.
Oil Analysis: Applied to wear monitoring and oil condition assessment, capable of predicting internal wear. Requires regular sampling and tracking of change trends.
Infrared Thermography: Applied to electrical connection and bearing temperature detection, offering non-contact, fast, and comprehensive advantages. Requires attention to environmental reflection and establishing thermal maps.
Motor Current Analysis: Applied to electrical fault and mechanical load monitoring, requires no additional sensors. Requires analyzing harmonic components to identify characteristics.
Conclusion
As a key piece of equipment in continuous production lines, the operational reliability of screw conveyors directly affects the stability of the entire production system. Through in-depth analysis and scientific classification of common failures, and by establishing systematic fault-diagnosis methods and maintenance strategies, equipment operational efficiency can be significantly improved, service life extended, and maintenance costs reduced.
Key Tip: Failures in screw conveyors are often the result of multiple factors working together. In practical fault handling, a systems-thinking approach should be adopted, comprehensively analyzing multiple dimensions such as material characteristics, equipment condition, operating conditions, and maintenance level, avoiding the one-sided repair approach of “treating the head when the head hurts, treating the foot when the foot hurts.”
With the development of IoT and intelligent monitoring technology, Prognostics and Health Management (PHM) for screw conveyors will become a future trend. By installing intelligent monitoring devices such as vibration sensors, temperature sensors, and current sensors, combined with big data analysis and artificial intelligence algorithms, early warning of faults and predictive maintenance can be achieved, elevating equipment management from reactive repair to a new stage of proactive prevention.
Article Word Count: Approximately 3,200 words
Keywords: Screw conveyor, Fault analysis, Bearing maintenance, Vibration diagnosis, Preventive maintenance
Intended Audience: Equipment maintenance engineers, Production management personnel, Mechanical design personnel
