Diagnosis and resolution of abnormal noise and vibration in industrial gearboxes

1. Problem description and scope

This technical manual details the systematic diagnostic procedure for industrial gearboxes (reducers/multipliers) that exhibit abnormal noise or vibration levels. An increase in noise or vibration levels is often the first symptom of impending mechanical failure. The scope of this guide covers spur, helical and bevel gear drives used in critical load applications.

The severity is classified as follows:

• Criticism: High-pitched metallic noise, vibration evident to the touch, sudden increase in temperature, visible particles in the oil. Requires immediate stop.
• Major: Change in vibration frequency profile, operating temperature above average, gradual increase in noise. Requires inspection within the next 24-48 hours.
• Minor: Mild noise or vibration consistent but slightly higher than baseline. Requires monitoring at the next scheduled maintenance.

2. Safety precautions

WARNING: Gearboxes store significant kinetic and thermal energy. Strict Lockout Tagout (LOTO) compliance is mandatory prior to any internal inspection. Always wear appropriate personal protective equipment (PPE): hearing protection, safety glasses, and thermal gloves. Do not make measurements on rotating components without adequate physical protection to avoid entrapment.

3. Diagnostic tools

4. Initial checklist

Before starting to open the reducer, record the following data:

5. Systematic diagnostic flow

1. Initial vibration analysis (Machine running):
   • If vibration is 1x RPM: Suspect misalignment or unbalance (shaft/coupling).
   • If the vibration is GMF (Gear Mesh Frequency): Suspect wear on gear teeth or pitch error.
   • If the vibration presents sidebands: Suspect eccentricity or bearing failure.
2. Thermal analysis:
   • Hot spot located in casing (bearing): Imminent bearing failure.
   • Uniform heat throughout the housing: Lubrication failure or overload.
3. Lubricant analysis:
   • If there is presence of ferrous particles: Severe wear on gears.
   • If the oil is degraded/dark: Oxidation due to excessive temperature.

6. Matrix of failures and causes

7. Root cause analysis

Misalignment: It is the main cause of excessive vibration. It causes additional radial and axial loads on the bearings, reducing their useful life exponentially. It is confirmed by laser alignment, verifying the parallelism and concentricity of the axes.

Fatigue Wear (Pitting/Spalling): Occurs due to overload or inadequate lubrication. Subsurface fatigue creates microcracks that evolve into material detachment. If not corrected, it destroys the geometry of the tooth.

Poor lubrication: Failure of the lubricating film causes metal-to-metal contact. This causes friction, temperature rise and cold welding (scoring/scuffing). Oil analysis will reveal an increase in non-ferrous particles and a drop in viscosity.

Excessive backlash: Results from accumulated wear on the flanks of the teeth. Produces knocks when reversing the load or varying the speed. The measurement is made by fixing a shaft and measuring the movement of the coupled shaft.

8. Resolution procedures

1. Alignment correction: Use laser alignment equipment. Adjust the motor/reducer supports using calibrated shims. Typical tolerance: <0.05 mm for high precision applications.
2. Gear repair: If the wear is slight, polishing can be done. If there is chipping or cracking, replacement of the affected gears is imperative (pinion and ring gear must be replaced as a pair to ensure contact).
3. Bearing Replacement: Remove the bearings using hydraulic pullers. Clean the housing and check interference settings. Install new bearings with thermal expansion method (induction heater, max temperature 100°C).
4. Backlash Adjustment: Adjust the center distance (if design allows) or replace components with gear sets ground to OEM specification.

9. Preventive measures

10. Spare parts and components

To purchase certified components, visit our technical catalog: https://www.unitecd.com/e-catalog/

11. References

• ISO 10816-3: Mechanical vibration in industrial machines.
• ISO 20816: General guide for the measurement and evaluation of vibration.
• UNITEC-D gear maintenance technical manual.
• UNE-EN 60204-1. industrial safety standards