1. Problem description & scope of application
This manual addresses gear noise (squealing, grinding, hitting) and abnormal vibrations in industrial gear drives. The target group is maintenance technicians and reliability engineers. The severity levels are classified as follows:
- Critical: Sudden change in noise level, metallic abrasion in the oil, uncontrolled temperature increase. Immediate system stop required.
- Major: Steady increase in vibrations over 4.5 mm/s (effective), slight heating. Inspection required within 24 hours.
- Minor: Slightly different running noises, no measurable vibration peaks. Monitoring as part of the next scheduled inspection.
2. Safety instructions
WARNING: Danger due to stored energy and rotating parts.
Before beginning each inspection, the gearbox must be switched off from the power supply in accordance with DIN EN 1037 (avoiding unexpected startup) and secured against being switched on again (lockout/tagout). When working on gearboxes with load torques, the load must be secured mechanically. Wearing personal protective equipment (PPE), including hearing protection, safety glasses and oil-proof gloves, is mandatory.
3. Diagnostic tools required
| tool | Specification | Measuring range/purpose |
|---|
| Vibration analyzer | FFT capable, ISO 10816 | 10Hz - 10kHz; Frequency spectrum analysis |
| multimeter | True RMS, CAT IV | Measuring operating temperature (with thermocouple) |
| Feeler gauge / dial gauge | Precision 0.01mm | Measurement of the backlash (backlash) |
| Oil analysis kit | Particle counting/spectrometry | Evidence of metallic wear |
| Endoscope | Industry standard, min. 5mm | Visual inspection of the tooth flanks without disassembly |
4. Checklist for initial intake
| Observation | Details |
|---|
| Operating condition | Load, speed, operating time since last oil change |
| Noise characteristics | Frequency (low/high), location (input/output), load dependency |
| Vibration levels | Veff (mm/s) in x, y, z direction |
| Oil temperature | Difference to ambient temperature |
| History | Date of last maintenance, alarms that occurred, changes to the load profile |
5. Systematic diagnostic flow
- Step 1: Vibration analysis (spectrum)
- Increased amplitudes at input speed -> Alignment problems or imbalance.
- Increased amplitudes at tooth meshing frequency (Zf) -> tooth wear, pitting or faulty gearing.
- Modulation at low frequencies -> bearing defects (rolling elements).
- Step 2: Oil Condition Test
- Presence of metal particles (aluminum, steel, bronze) -> Metallurgical damage analysis.
- Viscosity out of specification -> decomposition or incorrect lubricant.
- Step 3: Mechanical inspection
- Measuring the backlash using a dial gauge. Value outside OEM tolerance? -> Tooth wear.
- Endoscopic examination of the tooth flanks -> pitting, scuffing or fracture?
6. Error-cause matrix
| Symptom | Probable cause | Diagnostic test | Expected result |
|---|
| High IF amplitude | Tooth flank wear | Endoscopy | Pitting/removal visible |
| Imbalance/alignment error | Coupling defect / misalignment | Vibration measurement | Peaks at 1x rotation frequency |
| Bearing noise (grinding) | Bearing damage | Envelope analysis | Peaks in bearing frequencies |
| Banging sound | Broken tooth base | Endoscopy | Tooth fracture visible |
7. Root cause analysis
Tooth flank wear (pitting/seizing): Usually caused by insufficient lubrication or overloading. Leads to increased flank play and increased dynamic forces, which accelerates the damage pattern.
Bearing damage: Overload, inadequate lubrication or current continuity (EDM) lead to the destruction of the raceways. If not remedied, the transmission will become blocked.
8. Step-by-step repair
- Safety shutdown: Perform lockout/tagout.
- Dismantling: Provide access to the affected components.
- Component replacement: Replace defective bearings/gears according to OEM specifications.
- Setting: Set the backlash to the setpoint according to the manufacturer's data sheet.
- Verification: After assembly, carry out vibration measurement under load (reference value: Veff < 2.8 mm/s).
9. Preventive measures
| Cause | Strategy | Monitoring | interval |
|---|
| Lack of lubricant | Regular oil analysis | Oil level/condition | 3 months |
| Misalignment | Laser alignment | Vibration monitor | Annually |
10. Spare Parts & Components
| part | Specification | Change criterion | UNITEC Cat. |
|---|
| Rolling bearings | DIN 625 / DIN 720 | Bearing noise/vibration | Storage technology |
| Gasket set | Viton/NBR | Oil leakage | Sealing technology |
| Lubricant | ISO VG 220/320 | Oil analysis alarm | Lubricants |
To order spare parts, please visit our e-catalog: https://www.unitecd.com/e-catalog/
11. References
- DIN ISO 10816: Mechanical vibrations - evaluation of the vibrations of machines
- DIN 3990: Load capacity calculation of spur gears
- OEM Industrial Gearbox Manual (specific to each series)
