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Diagnosis and elimination of noise and vibration in industrial gearboxes: a practical guide

Technical analysis: Troubleshooting gearbox noise and abnormal vibration: oil analysis, gear wear patterns, backlash mea

Diagnosis and elimination of noise and vibration in industrial gearboxes: a practical guide

1. Description of the problem and scope

Abnormal noise (hum, grinding, knocking) and increased vibration in cylindrical, bevel-cylindrical and planetary gearboxes indicate the development of defects in mechanical components. This manual covers equipment with a nominal power from 11 to 500 kW used in Ukrainian industrial enterprises (metallurgical conveyors, cement mill drives, pumping stations and extruders).

Classification of criticality:

  • Critical (Level 3): The noise is accompanied by metallic grinding, vibration over 11.2 mm/s (RMS) at the shaft rotation frequency, or a sharp increase in the oil temperature above +85°C. Requires immediate equipment shutdown.
  • Significant (Level 2): An increase in the overall level of vibration in the range of 4.5–11.2 mm/s (RMS), the appearance of a periodic hum without stopping the production cycle. Diagnosis is required within 24–48 hours.
  • Minor (Level 1): Vibration level 1.8–4.5 mm/s (RMS), change in pitch. Requires monitoring and scheduling of inspection during the next scheduled maintenance.

2. Precautions and safety

CAUTION! DANGER OF INJURY AND ELECTRIC SHOCK!

Before performing any diagnostic work and disassembling the gearbox, perform the Lockout/Tagout (LOTO) procedure:

  • Completely de-energize the electric drive and lock the input machine in the off position with a padlock.
  • Block the mechanical part from involuntary rotation under the influence of potential energy (tensioned conveyor belts, vertical shafts) using mechanical stoppers or brakes.
  • Use personal protective equipment (PPE): safety glasses, heat-resistant gloves (when working with hot oil up to +80°C), special shoes with metal toes and protective headphones.
  • Be aware of the danger of hot surfaces of the gearbox housing and the working environment.

3. Necessary diagnostic tools

Name of the tool Specification / Model Measurement range Purpose
Vibroanalyzer Single/multi-channel (e.g., Fluke 810 or equivalent for ISO 10816/20816) 10 – 10000 Hz, 0.1 – 50 mm/s Total vibration measurement and spectral analysis of bearing/gear peaks
Thermal imager Infrared (sensitivity < 0.05°C) -20°C ... +250°C Detection of local overheating in the engagement zones and bearing assemblies
Digital multimeter True RMS (CAT III 1000V / CAT IV 600V) 0 - 1000 V, 0 - 10 A, 0 - 40 MΩ Checking the temperature sensors (Pt100) and the state of the grounding of the drive
Clock type indicator (IR) The price of the division is 0.01 mm with a magnetic stand 0 - 10 mm Measurement of axial and radial backlash of shafts, side gap in engagement
Lubricant analysis kit Portable spectrometer / ferrographic kit Detection of wear particles from 1 to 100 microns Determination of the concentration of iron, copper, chromium and the degree of oil degradation

4. Initial condition assessment checklist

The observation parameter Verification method Normal value Threshold value (Alarm)
The temperature of the gearbox housing Thermal imager / contact thermometer < +65°C (depending on the load) > +80°C or sharp gradient > 10°C/h
Oil level and condition Visually through the sight glass / sampling In the center of the window, transparent, without weight The presence of foam, darkening, metal powder, burning smell
Vibration on bearing supports Vibroanalyzer (directions H, V, A) < 1.8 mm/s (RMS) for ISO 10816-3 > 4.5 mm/s (warning), > 11.2 mm/s (accident)
External condition of oil seals and seals Visual inspection Dry, no streaks Active leakage of oil on the shaft or housing connectors

5. Systematic block diagram of diagnostics

  1. Symptom: The appearance of hum or vibration on the gearbox.
    • Check the vibration level and localization with a vibration analyzer.
      • If the vibration peak is at shaft rotational frequency (1X) or unbalance:
        • Check the couplings, shaft alignment, and motor/gear mounts to the frame.
          • Result: Loosening of bolts or angular/parallel displacement → Probable cause: Displacement of foundation bolts or wear of elastic coupling elements.
      • If vibration peaks at GMF - Gear Mesh Frequency and its harmonics:
        • Perform side clearance analysis and check tooth contact patch.
          • Result: Uneven contact patch or excessive backlash → Probable cause: Tooth wear, incorrect installation or deformation of shafts under load.
      • If the vibration peak at irregular high-frequency harmonics (BPFO, BPFI, BSF - bearing defect frequencies):
        • Perform a detailed spectral analysis of the acceleration envelope (Demodulation / PeakVue).
          • Result: Modulated bearing frequencies detected → Probable cause: Raceways or balls/rollers pitting.

6. Matrix of malfunctions and causes

Symptom Probable causes (by probability) Diagnostic test Expected result when confirming the cause
High-frequency squeal / hum, vibration at the GMF frequency 1. Wear or grinding of teeth (pitting)
2. Incorrect side clearance
3. Wheelbase shift		 Lubricant analysis for chips + clearance check with a clock-type indicator The presence of metal particles > 50 μm in size, the lateral gap differs from the nominal by > 40%
Low-frequency knock / hum (1 time per shaft revolution) 1. Damage to the rolling elements or bearing separator
2. Imbalance of idler shaft
3. Weakening of the key connection		 Spectral analysis of vibration (shaft orbit, demodulation) Presence of peaks at BPFI/BPFO frequencies with reversible frequency sidebands
Uniform hum at a high frequency, heating of the body 1. The oil does not meet the viscosity (ISO VG)
2. Shortage of oil
3. Gearbox overload		 Temperature measurement with a thermal imager + checking the brand of oil according to the passport Bearing temperature > +85°C, oil sample viscosity below nominal due to dilution or destruction
Sharp knocking noise when starting or reversing 1. Excessive side gap in engagement
2. Wear of clutch teeth
3. Axial movement of the shaft		 Measurement of axial backlash of shafts using IR The axial movement of the shaft exceeds the factory tolerance by 2-3 times

7. Analysis of the root causes of each malfunction

7.1. Gear teeth wear and pitting

Why it occurs: Occurs due to fatigue destruction of the working surfaces of the teeth under the action of cyclic contact stresses that exceed the endurance limit of the material (according to ISO 6336). Additional factors: contamination of the oil with solid particles or the use of oil with an inappropriate package of anti-seize additives (EP).

How to confirm: Endoscopic inspection through inspection hatches of the gearbox or analysis of an oil sample for the presence of ferromagnetic particles. Cracks (craters) or burrs are visible on the surface of the teeth.

Consequences: Progressive destruction of the tooth profile, engagement jamming, complete destruction of the gear wheel and production stoppage.

7.2. Rolling bearing defects

Why it occurs: The result of natural wear, improper installation, insufficient or excessive lubrication, as well as the flow of electric current through the bearing (electrofusion from frequency converters).

How to confirm: Vibroacoustic methods (measurement of impact peaks in decibels, SPM / PeakVue) and detection of bearing frequencies in the vibration spectrum.

Consequences: Bearing jamming, separator destruction, shaft misalignment and damage to adjacent gears due to a drop in rotational accuracy.

7.3. Violation of the geometry and alignment of the engagement

Why does it occur: Thermal deformations of the gearbox housing, insufficient stiffness of the foundation, errors in adjusting the bearings during the previous repair intervention according to the ISO 1328. standard

How to confirm: Checking the contact spot using paint (Berlin blue based paint - covering at least 60% of the length and 50% of the tooth height) and laser centering of the shafts.

Consequences: Edge contact of the teeth, overloading of one side of the tooth, rapid failure and cracks in the gear body.

8. Step-by-step troubleshooting procedures

Procedure 1: Replace the damaged bearing and adjust the clearance

  1. Perform the LOTO procedure, pour the oil into a special container.
    • Check: make sure there are no remaining lubricants in the crankcase.
  2. Remove the bearing caps and pull out the shaft assembly using special pullers or hydraulic equipment.
    • Control: do not allow hammer blows on the landing surfaces of the shafts.
  3. Remove the old bearing using an induction heater or hydraulic puller.
    • Control: check the seating diameter of the shaft neck with a micrometer (tolerance according to ISO h6/j6).
  4. Heat the new bearing to a temperature no higher than +110°C using an induction heater and mount it on the shaft as far as it will go.
    • Check: measure the radial clearance of the bearing with a feeler gauge according to the manufacturer's technical documentation.
  5. Assemble the assembly, adjust the axial tension of the bearings with adjusting shims with an accuracy of 0.05 mm.
    • Control: the moment of resistance to rotation of the shaft must comply with the factory regulations.
  6. Fill in fresh transmission oil of the recommended viscosity class (eg ISO VG 220 or 320 according to ISO 3448).
    • Control: check the level through the sight glass after 10 minutes of settling.

Procedure 2: Checking and repairing the contact patch in the clutch

  1. Clean the working surfaces of the gear teeth and wheels from oil residues using a special cleaner.
    • Control: surfaces must be completely degreased.
  2. Apply a thin layer of paint (azure) to 3-4 teeth of the drive gear.
    • Control: layer should be uniform, without overflows.
  3. Rotate the idler shaft by hand in both directions under a slight braking torque.
    • Control: rotate 1 full turn of the wheel.
  4. Assess the impression of the paint on the driven tooth.
    • Norm: the contact spot is concentrated in the center of the tooth, occupying at least 60% of its length and 50% of its height.
  5. If the spot moves to the edge, adjust the position of the shaft using adjusting washers or moving the bearing housing.
    • Control: repeat the dyeing test until the regulatory indicators are reached.

9. Preventive measures

The root cause Prevention strategy Monitoring method Recommended interval
Tooth wear and oil degradation Use of high-quality synthetic lubricants (PAO/PG) with EP additives, moisture control Laboratory analysis of oil (ISO 4406 to determine purity) Every 2000 hours or 6 months
Fatigue failure of bearings Maintaining cleanliness during installation, protection against currents on the shaft (insulated bearings) Continuous vibration monitoring (online sensors or manual control) Monthly (manual) / continuously (online)
Shift and misalignment of shafts Laser centering of the drive taking into account thermal expansion Inspection by indicators or laser systems Every 12 months or after repairs

10. Spare parts and components

Description of the part Specification When to replace Category UNITEC
Radial thrust roller bearings Series 320xx, 322xx (e.g. SKF / FAG according to DIN 616) When BPFI/BPFO vibration level increases or metal in the oil Industrial bearings
A set of cuff seals (seals) FKM (Viton) or NBR with anther for DIN 3760 Every time the gearbox is disassembled or there are oil leaks Seals and oil seals
Gear pairs (gears and wheels) According to the customer's drawing, module m=2...25, hardened teeth When the tooth profile is worn > 15% or pitting appears on the area > 25% Components of reducers
Transmission synthetic oil ISO VG 220 / 320 ( CLP HC / CLP PG ) After 5000–8000 hours of operation (depending on the temperature regime) Lubricating materials

To order certified spare parts with delivery to your company, visit the electronic catalog UNITEC-D.

11. Normative references

  • ISO 10816-3 / ISO 20816-3: Mechanical vibration. Evaluation of machine vibration by measurements on unaccounted parts.
  • ISO 6336: Calculation of the strength of cylindrical gears.
  • ISO 1328-1: Cylindrical gears. Accuracy tolerance system.
  • DSTU GOST 21354: Cylindrical gears. Strength calculation (or relevant European EN standards).
  • Technical safety regulations of machines and equipment (CE certification, UkrSEPRO).

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