Problem description and scope
This manual is intended for diagnosing and eliminating noise and abnormal vibrations in industrial gearboxes. Symptoms include increased noise (over 85dB), vibration over 4.5mm/s, torque instability and increased gear housing temperature over 80°C.
Field of application:
- Cylindrical and conical reducers with a capacity of 1-500 kW
- Worm transmissions of industrial equipment
- Planetary reducers of conveyor systems
- Gearboxes of metalworking machines
Classification of criticality:
- Critical: Vibration >7.1 mm/s, noise >90 dB, temperature >90°C
- Important: Vibration 4.5-7.1 mm/s, noise 85-90 dB, temperature 80-90°C
- Minor: Vibration 2.8-4.5 mm/s, noise 75-85 dB, temperature 70-80°C
Safety measures
ATTENTION! Before starting diagnostics:
- Apply the LOTO (lockout/tagout) procedure
- Use PPE: safety glasses, gloves, hearing protection
- Accumulated Energy: Relieve pressure in hydraulic systems
- Rotating parts: Full stop before removing manhole covers
- Hot grease: The temperature can reach 100°C
- Chemical hazard: Vapors of used lubricant in enclosed spaces
Diagnostic equipment is required
| Tool | Specification | Measurement range | Purpose |
|---|---|---|---|
| Vibroanalyzer | SKF CMVA 65, Fluke 805 | 0.1-1000 mm/s | Measurement of general vibration and spectral analysis |
| Sound meter | Class 2 according to IEC 61672 | 30-130 dB | Sound pressure level control |
| Thermal imager | The resolution is 160×120 | -20°C to +250°C | Detection of local overheating |
| Backlash probes | Set 0.05-1.0 mm | ±0.02 mm accuracy | Measurement of side play of teeth |
| Endoscope | Diameter 6-8 mm, length 1 m | - | Internal inspection of gears |
| Mechanical stethoscope | - | - | Localization of noise sources |
| Lubricant selection kit | Syringe, test tubes | 50-100 ml | Sampling for analysis |
Initial assessment checklist
| Parameter | What to observe/record | norm | Anxiety |
|---|---|---|---|
| Total Vibration (RMS) | Measure on the housing near the bearings | <2.8 mm/s | >4.5 mm/s |
| Noise level | At a distance of 1 m from the gearbox | <75 dB | >85 dB |
| Body temperature | The hottest point of the body | <70°C | >80°C |
| Lubrication level | The position of the level indicator | Between min./max. | Below the minimum |
| External sources | Traces of grease under the gearbox | Absent | Available | >
| The load | % of the nominal torque | 70-100% | >110% |
Systematic diagnostics - decision-making scheme
1. Analysis of the nature of noise and vibrations
- Periodic noise with the frequency of rotation of the input shaft
- IF the frequency coincides with nvh - eccentricity of the gear
- IF it is accompanied by shocks - a gear tooth defect
- Go to point 3.1 (Diagnostics of gears)
- Periodic noise with the frequency of rotation of the output shaft
- IF the frequency coincides with the nth - eccentricity of the wheel
- IF the vibration increases under load - wear of the wheel teeth
- Go to point 3.1 (Diagnostics of gears)
- High frequency noise and vibration
- IF frequency >1000 Hz - rolling bearings
- IF the frequency is 500-1000 Hz - sliding bearings
- Go to point 3.2 (Diagnostics of bearings)
- Constant noise without a clear frequency
- IF it changes with the viscosity of the lubricant - insufficient lubrication
- IF accompanied by an increase in temperature - overheating
- Go to point 3.3 (Lubricant analysis)
2. Spectral analysis of vibrations
Settings of the vibration analyzer:
- Frequency range: 10-10000 Hz
- Number of spectrum lines: 3200
- Window: Hanning
- Averaging: 4 spectra
Matrix of causes of malfunctions
| Symptom | Probable cause (by probability) | Diagnostic test | Expected result upon confirmation |
|---|---|---|---|
| Intermittent noise at the engagement frequency | 1. Wear of teeth (70%) 2. Incorrect centering (20%) 3. Lubricant contamination (10%) |
Endoscopic examination + lubricant analysis | Traces of pitting on the teeth + metal shavings in oil |
| Vibrations at the shaft rotation frequency | 1. Imbalance (60%) 2. Unawareness (30%) 3. Shaft deformation (10%) |
Vibrations in the radial direction | Peaks at 1×RPM in horizontal and vertical directions |
| High frequency vibrations | 1. Bearing defects (80%) 2. Poor lubrication (15%) 3. Pollution (5%) |
Spectral analysis of the envelope | Peaks on BPFO, BPFI, BSF or FTF |
| Housing overheating >80°C | 1. Insufficient cooling (40%) 2. Overload (35%) 3. High friction in engagement (25%) |
Thermal imaging examination + load control | Local hot spots >90°C near bearings/engagement | >
| Metallic knock when starting | 1. Large side play (50%) 2. Bearing wear (30%) 3. Weakening of fastenings (20%) |
Backlash measurement with feelers | Clearance >0.3 mm for a 3-5 mm module |
Detailed analysis of the main causes of malfunctions
3.1 Gear wear and damage
Pitting (pitting):
Occurs due to contact fatigue of tooth surfaces when permissible contact stresses are exceeded. Critical pressure: >1500 MPa for 40KHN steel.
Diagnosis:
- Visual inspection through inspection hatches
- Endoscopic control of inaccessible areas
- Lubricant analysis for iron content >150 ppm
Abrasive wear:
The reason: contamination of the lubricant with particles >40 microns. Cleanliness class must be ISO 4406 level 19/17/14.
Measurement of side play:
- Lock one wheel
- Measure the angular backlash of the second wheel
- Calculate the linear backlash: L = α × R (α in radians, R is the radius of the circle)
- Compare with the norm: 0.15-0.25 mm for a 3-5 mm module
3.2 Diagnostics of bearings
Characteristic frequencies of bearing defects:
- BPFO (outer ring defect) = 0.4 × n × z
- BPFI (inner ring defect) = 0.6 × n × z
- BSF (rolling body defect) = 0.4 × n × z × (D/d)
- FTF (separator defect) = 0.4 × n
where n is the rotation frequency (Hz), z is the number of rolling elements, D/d is the diameter ratio
Temperature diagnostics:
- Normal operation: 40-60°C
- Warning: 60-80°C
- Emergency condition: >80°C
3.3 Analysis of the condition of the lubricant
Main indicators to monitor:
| Parameter | norm | Warning | Critical condition |
|---|---|---|---|
| Viscosity at 40°C, mm²/s | ±10% of nominal | ±15% of nominal | ±25% of nominal |
| Iron content, ppm | <50 | 50-150 | >150 |
| Water, % | <0.1 | 0.1-0.5 | >0.5 |
| Acid value, mg KOH/g | <2 | 2-4 | >4 |
| Purity class ISO 4406 | 19/17/14 | 20/18/15 | >21/19/16 |
Step-by-step troubleshooting procedures
4.1 Elimination of gear wear
- For minor pitting (<10% of the tooth surface):
- Reduce the load to 80% of the nominal
- Replace the oil with a viscosity grade one step higher
- Install an additional fine filter ≤25 μm
- Inspection after 500 hours of operation
- For significant wear (>10% of the tooth surface):
- Stop the equipment
- Measure the remaining thickness of the tooth with a caliper
- IF the thickness is <80% of the nominal - replace the gear wheel
- Check the centering of the shafts with a tolerance of ±0.05 mm
- Adjustment of side clearance after replacement:
- Set clearance 0.20±0.05mm for 3-5mm module
- Use adjusting spacers with a thickness of 0.1-0.5 mm
- Tightening moment of cover bolts: 150-200 Nm
4.2 Replacement of bearings
- Dismantling:
- Heating the body to 80-100°C with an induction heater
- Use the puller with even force
- Clean the seating surfaces with solvent
- Seating control:
- Shaft ovality: <0.01 mm
- Surface roughness: Ra 0.8-1.6 μm
- Radial runout: <0.02 mm
- Installation of new bearings:
- Heating the bearing to 80°C in an oil bath
- Installation time: no more than 2 minutes after heating
- Axial tension: 0.02-0.05 mm for the case
- Filling with lubrication: 30-50% of the internal volume
4.3 Lubricant replacement and cleaning
- Complete oil change:
- Drain the used oil through the drain plug
- Flush the housing with flushing grease for 30 minutes
- Fill with fresh grease up to the level of the indicator
- Run the gearbox at idle speed for 15 minutes
- Refueling volume by types of gearboxes:
- Cylindrical single-stage: 2-5 liters
- Cylindrical two-stage: 5-15 liters
- Worm: 1-8 liters
- Planetary: 3-12 liters
Preventive measures
| The reason for the malfunction | Prevention strategy | Control method | Recommended interval |
|---|---|---|---|
| Tooth wear | Load control ≤100% of nominal | Endoscopic examination | Every 2000 hours |
| Lubricant contamination | Filtering ISO 4406 19/17/14 | Analysis of lubricant samples | Every 1000 hours |
| Bearing defects | Temperature control <70°C | Vibrodiagnosis | Every 500 hours |
| Misalignment of the shafts | Accurate centering during installation | Control of clutches with a laser centerer | With every repair |
| Gearbox overheating | Cleaning the cooling fins | Thermal imaging control | Every 3 months |
Spare parts and components
| Description of the part | Specification | When to replace | Category UNITEC |
|---|---|---|---|
| Ball bearings | SKF 6000-6400 series | With vibrations >7 mm/s or heating >80°C | Rolling bearings |
| Roller bearings | SKF NU, NJ series | When metal shavings appear in the oil | Rolling bearings | >
| Shaft sealing | NBR 70-90 Shore A | In case of oil leaks | Sealing elements |
| Industrial lubricant | ISO VG 220-460 | Every 4,000-8,000 hours or with KCH >4 mg KOH/g | Lubricating materials |
| Filter elements | Fineness of filtration is 25 microns | When the pressure drop is >0.5 bar | Filters and separators |
| Magnetic stoppers | NdFeB neodymium magnets | In case of mechanical damage | Accessories for reducers | >
To order spare parts, visit our electronic catalog: https://www.unitecd.com/e-catalog/
Reference materials
- DSTU 2860-94 "Cylindrical gears. Strength calculation"
- ISO 14635-1:2000 "Gears - FZG test procedures"
- ISO 10816-3:2009 "Mechanical vibration - Evaluation of machine vibration by measurements on non-rotating parts"
- EN 13824:2004 "Condition monitoring and diagnostics of machines - General guidelines"
- ISO 4406:2017 "Hydraulic fluid power - Fluids - Method for coding the level of contamination by solid particles"
- UNITEC-D industrial gearbox maintenance manual
- Manual on vibration diagnostics of mechanical equipment
