1. Problem Description and Scope
Sudden blocking and overloading of a chain conveyor represent critical failure conditions that compromise production continuity and put the structural integrity of the system at risk. This document guides the maintenance technician in systematically identifying root causes. Scenarios covered include critical chain stretch, sprocket wear, lubrication failure, and foreign material buildup in the slide path.
Severity classification: Critical (risk of total line stoppage, chain breakage or irreversible damage to the gearmotor).
2. Safety Precautions
ATTENTION: Before starting any diagnostic or repair activity, it is mandatory to implement the Lockout/Tagout (LOTO) procedure. Completely isolate the gearmotor's electrical power supply and discharge any accumulated mechanical energy (chain tension). The use of Personal Protective Equipment (PPE) compliant with UNI EN ISO standards (cut-proof gloves, safety footwear, protective glasses) is essential. Do not attempt to clear jams while the system is powered on.
3. Diagnostic Tools Required
| Tool | Specification/Model | Range/Accuracy | Purpose |
|---|---|---|---|
| Digital caliper | IP67, 0-300mm | 0.01mm | Elongation measurement (chain pitch) |
| Multimeter | True RMS | 0-20A AC | Motor amperometric absorption measurement |
| Thermal imaging camera | Range -20/+500°C | ±2°C | Identification of friction/overheating points |
| Optical speedometer | Lasers | 1-99999RPM | Check shaft rotation speed |
| Vibrometer | Standard ISO 10816 | 10-1000Hz | Analysis of bearing wear and misalignment |
4. Initial Assessment Checklist
| Observation | Action/Check | Record |
|---|---|---|
| Operating Conditions | Check whether the load is within nominal limits | Current load vs nominal load |
| Alarm History | Analyze the PLC/Inverter log | Error codes, timestamps |
| Noise | Inspect visually and acoustically | Type of noise (squealing, banging) |
| Lubrication status | Check presence and viscosity of lubricant | Level, color, contamination |
5. Systematic Diagnostic Flow
- Symptom: Motor absorption higher than nominal.
- Check material accumulation in the path. If present → Remove and clean.
- If there is no material → Check the alignment of the pinions. If misaligned → Realign.
- If alignment correct → Examine lubrication.
- Symptom: Rhythmic noise or knocking during rotation.
- Check the pinions for wear. If sharp or asymmetrical teeth → Replace sprockets.
- If sprockets are intact → Check chain elongation (measure on 10 links). If elongation > 2.5% → Replace chain.
6. Fault-Cause Matrix
| Symptom | Probable Causes (Ranking) | Diagnostic Test | Expected Result if Confirmed |
|---|---|---|---|
| Sudden blocking | 1. Material jam; 2. Broken pin | Visual inspection; Vibration analysis | Physical obstruction; Vibrational peak |
| Motor overload | 1. Lack of lubrication; 2. Stretched chain | Thermal imaging camera; Chain pitch measurement | Hot spots > 80°C; Elongation > 2% |
| Metallic noise | 1. Pinion wear; 2. Misalignment | Visual inspection; Check gauges | Worn teeth; Misalignment > 0.5mm |
7. Root Cause Analysis
7.1 Chain Lengthening
Caused by progressive wear of the pins and bushes. Spent or contaminated lubricant acts like abrasive paste, accelerating wear. If not corrected, it causes skipping of the teeth on the sprockets and catastrophic failures.
7.2 Wear of the Sprockets
Direct result of an incorrect fit with a worn chain or poor cross alignment. Excessive wear transforms the tooth profile, reducing the contact area and increasing point stress.
8. Resolution Procedures
- Chain Replacement:
- Perform LOTO.
- Release the tensioner.
- Remove the worn chain using suitable tools (chain wrench).
- Install the new chain, checking the correct mounting direction (if applicable).
- Adjust the tension according to the manufacturer's data (e.g. 10-15mm deflection).
- Sprocket realignment:
- Use a laser ruler or taut wire to check the coplanarity of the sprockets (tolerance ±0.2mm).
- Adjust the axial position on the gearmotor/driven shaft.
- Check the tightening of the fixing screws (torque defined by the OEM manual).
9. Preventive Measures
| Root Cause | Strategy | Monitoring Method | Interval |
|---|---|---|---|
| Lubrication | Automatic lubrication | Visual oil analysis | Weekly |
| Wear | Predictive maintenance | Vibration/pitch analysis | Monthly |
10. Spare Parts and Components
| Description | Specify | When to Replace | Category |
|---|---|---|---|
| Roller chain | ISO 606 | Elongation > 2.5% | Transmission |
| Pinion | C45 steel | Tooth wear > 10% | Transmission |
| Lubricant | Grease EP NLGI 2 | Contamination/Drying | Maintenance |
To purchase original spare parts, consult our electronic catalogue: https://www.unitecd.com/e-catalog/
11. References
- UNI ISO 606: Precision roller chains.
- ISO 10816: Mechanical vibrations.
- Specific OEM service manuals.
