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Diagnostics and Troubleshooting Guide: Noises and Abnormal Vibrations in Gear Units

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

1. Description of the problem and scope of application

This manual is intended for the diagnosis and troubleshooting of abnormal noises and vibrations in industrial gearboxes. These symptoms are often the first signs of potentially critical component failures such as bearing, gear or lubrication problems. Timely and accurate diagnostics are critical to prevent catastrophic failures that lead to equipment downtime and significant financial losses.

This document covers the following types of equipment: worm gears, cylindrical gears, bevel gears, planetary gears used in a wide range of industrial applications (conveyors, pumps, mixers, extruders, etc.).

Classification of the severity of the malfunction:

  • Critical: Sharp, loud noise (bang, screech), intense vibration with an amplitude greater than 10 mm/s (RMS) or rapid temperature rise (> 90°C). Immediate shutdown of the equipment is mandatory.
  • Significant: Constant, unusual noise (buzzing, howling, clicking) or vibration in the range of 4.5-10 mm/s (RMS). A scheduled inspection stop is recommended.
  • Minor: Slight, intermittent noise or slight increase in vibration (2.8-4.5 mm/s RMS) which may indicate initial wear. Enhanced monitoring is needed.

2. Precautions

⚠ SAFETY WARNING ⚠
Before starting any diagnostic work, ensure that the equipment is completely de-energized and locked out according to the LOTO (Lockout/Tagout) procedure. Check the absence of electrical voltage with the help of appropriate devices. Be aware of stored energy in springs, hydraulic or pneumatic systems. Use personal protective equipment (PPE): safety glasses, headphones, gloves, work shoes with metal toes. Hot surfaces, pressurized lubricants and moving parts present a risk of injury.
⚠ ALWAYS FOLLOW THE EQUIPMENT MANUFACTURER'S SAFETY INSTRUCTIONS ⚠

3. Necessary diagnostic tools

For effective diagnosis of gear noise and vibration, specialized tools are required:

Tool Specification/Model Measurement range Purpose
Vibration analyzer For example, SKF Microlog, Fluke 810 Velocity (0.1-500 mm/s RMS), Acceleration (0.1-50 g RMS), Frequency (10 Hz - 20 kHz) Measurement of the general level of vibration, spectral analysis to identify sources (bearings, teeth, imbalance)
Acoustic stethoscope (electronic/mechanical) For example, SKF TMST 3, Fluke 910 Audio range, noise amplification Localization of the noise source in the gearbox (bearings, teeth)
Thermal imaging camera For example, Fluke Ti480, FLIR T-Series From -20°C to +650°C, accuracy ±2°C Detection of abnormal heating associated with friction, lack of lubricant, overload
Lubricant analysis kit Sampling according to ISO 14597 Viscosity, water content, wear particles (Fe, Cu, Cr), additives, acidity Assessment of the condition of the lubricant, the presence of impurities and wear metals
Set of probes (feller probes) The range is 0.02 mm - 1.0 mm Measurement of clearances, backlashes, inspection of connections Measurement of side clearance of gears (backlash)
Clock-type indicator with a stand Range 0-10 mm, accuracy 0.01 mm Measurement of runout, axial/radial backlash, alignment of shafts Accurate measurements of clearances and alignment
Borescope (endoscope) The diameter of the probe is 5-10 mm, the length is up to 3 m Visual inspection of internal components without disassembly Inspection of the condition of teeth, bearings, internal surfaces for wear, pitting, chips
Multimeter (with current measurement function) Range up to 1000 V AC/DC, up to 10 A AC/DC Measurement of electric motor current Detection of motor overload, which may indicate increased friction in the gearbox

4. Initial evaluation checklist

Before starting detailed diagnostics, it is necessary to collect raw data and conduct a visual inspection. This will help narrow down the range of potential malfunctions.

Observation/Action What to write down Diagnostic value
Type and nature of noise Humming, screeching, clicking, howling, knocking, periodicity, does it change with load/speed Each type of noise indicates different sources of malfunction (humming - gears, grinding - bearings)
Visual inspection of the gearbox The presence of oil leaks, cracks on the housing, weakened fasteners, deformations, foreign objects Oil leaks lead to oil starvation; weakened fasteners - to increased vibration
The temperature of the gearbox housing Measure with a thermal imager or non-contact thermometer at different points. Compare with normal (< 80°C) Excessive heating (local or general) indicates excessive friction, overload, lack of lubrication
Lubrication level Check with a dipstick or sight glass. Record color, transparency, presence of sediment/foam A low level or degradation of lubricant is a probable cause of malfunctions
Service history Date of the last oil change, type of oil, previous repairs, component replacements May indicate late maintenance or repeated malfunctions
Terms of use Load (current, maximum), rotation speed, duty cycles, environmental impact Overloading, shock loads, aggressive environments accelerate wear
History of accidents and warnings Переглянути журнали автоматизованих систем керування May contain early signs of a problem

5. Systematic diagnostic algorithm

This algorithm will help to systematically identify the source of noise and vibration.

  1. Initial evaluation and security:
    1. Follow the steps in section 4. Initial Evaluation Checklist.
    2. Make sure all Precautions (Section 2) are followed.
    3. Determine the nature of noise and vibration:
      • If the noise is sharp, knocking, grinding, and the vibration is intense (> 10 mm/s RMS) - immediately stop the equipment. Go to point 6.
      • If the noise is constant buzzing/howling, and the vibration is 4.5-10 mm/s RMS, continue the diagnosis.
      • If the noise is periodic or the vibration is 2.8-4.5 mm/s RMS – increased monitoring, scheduled diagnostics.
  2. Diagnostics using a vibration analyzer:
    1. Install accelerometers on the gearbox housing in the radial and axial directions, near the bearings and gears.
    2. Measure the overall level of vibration (velocity, mm/s RMS) and acceleration (g RMS).
    3. Perform a vibration spectral analysis.
      • If the vibration peaks are observed at frequencies multiples of the rotation frequency of the shafts (1X, 2X, 3X):
        • Probable cause: Imbalance or misalignment of the shafts.
        • Action: Check shaft alignment (chapter 7.1) and rotor balancing. Go to point 3.
      • If vibration peaks are observed at characteristic bearing frequencies (BPFI, BPFO, BSF, FTF):
        • Probable cause: Bearing wear or damage.
        • Action: Use the acoustic stethoscope to locate. Go to point 4.
      • If vibration peaks are observed at GMF and their harmonics:
        • Probable cause: Tooth wear, incorrect clearance, tooth damage.
        • Action: Go to point 5.
      • If the vibration is broadband, has no clear peaks:
        • Probable cause: Oil starvation, cavitation, loose mounts, resonance.
        • Action: Go to point 6.
  3. Diagnostics of misalignment of shafts:
    1. Measure the misalignment of the motor and gearbox shafts using a clock-type indicator.
    2. Criteria: Allowable radial and axial misalignment should not exceed 0.05 mm for speeds up to 1500 rpm. For higher speeds, the requirements are stricter (0.02-0.03 mm).
    3. If misalignment exceeds the norm:
      • Probable cause: Shaft misalignment.
      • Action: Perform fine alignment (section 8.1).
  4. Bearing diagnostics:
    1. Use an acoustic stethoscope to locate the noise on the gear housing, especially near the bearing assemblies.
    2. Estimate the temperature of the bearing units using a thermal imager. Norm: the temperature of the bearing should not exceed the ambient temperature by more than 40°C, and be lower than 90°C.
    3. Analyze the lubricant for the presence of wear metals (Fe, Cr, Mn - for steel bearings; Cu, Pb, Sn - for bronze separators/bushings).
    4. If the stethoscope detects grinding/rustling, the thermal imager - local overheating, the analysis of the lubricant - an increased content of wear metals:
      • Probable cause: Bearing wear or damage.
      • Action: Disassembly, visual inspection, replacement of bearings (chapter 8.2).
  5. Diagnosis of gears:
    1. Measure the backlash of the gears using feelers or a watch-type indicator. The regulatory gap is specified in the manufacturer's documentation. Usually 0.08-0.25 mm for small-medium gears.
    2. Perform a visual inspection of the teeth through inspection hatches or with a borescope (if available). Шукайте сліди піттингу, сколів, вибоїн, надмірного зносу, зміщення контактної плями.
    3. Analyze the lubricant for the presence of wear metals (Fe, Sn – for steel teeth; Cu, Pb – for bronze worm pairs).
    4. If the gap is greater than the norm, the teeth are visually damaged, or the oil analysis shows a significant content of wear metals:
      • Probable cause: Gear wear, damage or improper adjustment.
      • Action: Disassembly, repair/replacement of gears, adjustment of clearance (chapter 8.3).
  6. Diagnostics of the lubrication system and other causes:
    1. Perform a complete lubrication analysis (section 7.4).
    2. Check the strength of fastening the gearbox to the foundation, as well as the fastening of covers and other housing elements. Tighten the bolts according to the regulations.
    3. If oil analysis shows degradation, contamination, excessive water, low level:
      • Probable cause: Lubricant problems (low level, contamination, wrong type).
      • Action: Replacement of lubricant, filters, elimination of leaks (chapter 8.4).
    4. If fasteners are loose:
      • Probable cause: Loose fasteners.
      • Action: Tighten fasteners, check the foundation.

6. Malfunction-cause matrix

Ця таблиця допоможе співвіднести симптоми з найбільш імовірними причинами, тестами та очікуваними результатами.

Symptom Probable causes (in order of decreasing probability) Diagnostic test Expected result if the cause is confirmed
Constant buzzing/howling that changes with load
  1. Gear wear (pitting, abrasive wear)
  2. Incorrect clearance (backlash) of gears
  3. Misalignment of the shafts
  4. Lubricant degradation (loss of viscosity)
 Vibration analysis (GMF), Borescope, Backlash measurement, Lubrication analysis
  • GMF peaks, visible tooth wear, increased Fe in lube
  • Backlash is not allowed
  • Misalignment > 0.05 mm
  • Low viscosity, increased acidity of the lubricant
A rustling, screeching, rattling noise that increases with load/speed
  1. Bearing wear or damage
  2. Insufficient bearing lubrication
  3. Excessive bearing preload
  4. Entry of foreign particles
 Acoustic stethoscope, Thermal imager, Vibration analysis (BPF), Lubrication analysis
  • Noise localized in bearings, local overheating (> 90°C), peaks on BPF, increased Fe/Cr
  • Signs of oil starvation
  • Increased temperature, severe vibration
  • Visible particles in the lubricant
Knocking, clicking, occasional knocks
  1. Broken or chipped teeth
  2. Splined joints are worn
  3. Loose fasteners (reducer to the foundation, covers)
  4. Excessive backlash in the bearings
 Visual inspection, Borescope, Fastening tightening check, Backlash measurement
  • Visible teeth damage
  • Backlash in slots, increased level of vibration at impact frequencies
  • Loose bolts
  • Backlash of bearings > 0.1 mm
General increased vibration (broadband)
  1. Misalignment of shafts
  2. Imbalance of rotating parts
  3. Loose fasteners/foundation
  4. Resonance
 Vibration Analysis (1X, 2X, 3X), Alignment Measurement, Fastener Inspection
  • Peaks at 1X, 2X, 3X, discrepancy > 0.05 mm
  • Peaks at 1X, eccentricity
  • Loosen bolts, gearbox movement
  • High vibration at the natural frequencies of the system
Increased temperature of the gearbox
  1. Insufficient lubricant level or degradation of lubricant
  2. Excessive friction in bearings or gears
  3. Gearbox overload
  4. Wrong type of lubricant
 Thermal imager, Lubricant analysis, Load check, Lubricant type check
  • Temperature > 90°C, low lubrication level, degradation
  • Local overheating, increased vibration
  • The motor current exceeds the rated current
  • The viscosity of the lubricant does not meet the requirements

7. Root cause analysis for each malfunction

7.1. Misalignment of the shafts

Explanation: Misalignment occurs when the axes of rotation of the motor and gearbox shafts do not lie on the same straight line. It can be a parallel, angular or combined displacement. The main reasons are: incorrect installation, deformation of the frame, thermal deformation, wear of the coupling. This results in cyclic stress on the shafts, bearings and seals, causing excessive friction and vibration.

How to confirm: Misalignment measurement using a laser alignment system or two watch-type indicators. Critical indicator: radial or angular displacement greater than 0.05 mm for most industrial applications. Additionally, the vibration spectrum analysis will show the dominant peaks at 1X, 2X, 3X rotation frequency.

Potential damage: Premature wear of bearings, shaft seals, coupling, shaft fatigue, possible shaft breakage during long-term operation. It can also cause local overheating, diagnosed by a thermal imager.

7.2. Bearing wear or damage

Explanation: Bearings are critical components that support shafts and reduce friction. Wear can be caused by insufficient or incorrect lubrication, contamination of the lubricant, improper installation (shock loads during installation), overloading, vibration or material fatigue. Damage includes pitting, pitting, abrasive wear, and fretting corrosion.

How to confirm:

  • Acoustic analysis: Rustling, grinding, clicking localized near the bearing using a stethoscope.
  • Vibration analysis: The vibration spectrum will show the characteristic frequencies of the bearings (BPFI, BPFO, BSF, FTF) and their harmonics. The overall vibration level exceeds 4.5 mm/s RMS.
  • Thermography: Local overheating of the bearing assembly (> 90°C).
  • Lubricant analysis: Increased content of wear metals (Fe, Cr, Mn for steel, Cu for separators) and particles larger than 5 microns.
  • Visual inspection (after disassembly): Pitting, sinks, tread wear, separator damage, discoloration.

Potential Damage: Increased friction, overheating, shaft jamming, damage to bearing seats, damage to gears due to shaft displacement. It is possible to destroy the gearbox housing.

7.3. Gear wear or damage

Explanation: Gears transmit torque. Their wear can be caused by constant overloading, shock loads, insufficient lubrication, aggressive environment, abrasive particles in the lubricant, fatigue of the material. Common types of wear: pitting (surface fatigue), abrasive wear, adhesive wear (seizing), plastic deformation, over-scoring, tooth breakage.

How to confirm:

  • Acoustic analysis: Humming, howling, grinding, which changes with the load. Knocking when the teeth break.
  • Vibration analysis: Vibration peaks at tooth engagement frequencies (GMF) and their harmonics. Additional sidebands around the GMF may indicate wear modulation.
  • Visual inspection (through a borescope or after disassembly): Detection of pitting (pits on the surface of the teeth), seizing, chips, cracks, abrasive scratches.
  • Backlash measurement: Backlash that exceeds the norm (eg > 0.3 mm for medium gears) indicates excessive wear.
  • Lubricant analysis: Increased content of wear metals (Fe, Sn) and large particles.

Potential damage: Reduced transmission efficiency, increased noise and vibration, gear jamming, teeth and housing destruction, catastrophic failure.

7.4. Oil problems

Explanation: Lubricant performs the functions of friction reduction, cooling, dirt removal and corrosion protection. Problems include: low oil level, oil degradation (oxidation, loss of additives), contamination (water, dust, metal particles), use of the wrong type of oil. All these factors critically affect the service life of bearings and gears.

How to confirm:

  • Visual inspection: Low oil level, discoloration, cloudiness, presence of sediment or foam.
  • Lubricant analysis (according to DSTU ISO 2909, DSTU ISO 3104):
    • Viscosity: Viscosity change (increase or decrease) beyond ±10% of the initial one.
    • Water content: > 0.05% for most oils.
    • Acid number (AN): Increase in AN by more than 0.5 mg KOH/g.
    • Spectral analysis: Increased content of wear metals (Fe, Cu, Cr), polluting elements (Si - dust).
    • Particle Counter: Purity Class ISO 4406:1999 (usually no higher than 18/15/12 for reducers).
  • Thermography: General overheating of the gearbox due to increased friction.

Potential damage: Accelerated wear of gears and bearings, corrosion, overheating, increased energy consumption, rapid destruction of components.

8. Step-by-step troubleshooting procedures

8.1. Correction of misalignment of shafts

  1. ⚠ SECURITY: Follow the LOTO procedure.
  2. Clean the bearing surfaces under the motor and gearbox.
  3. Disconnect the coupling connecting the shafts.
  4. Use a laser leveling system or two watch-type indicators to accurately measure misalignment.
  5. Adjust the position of the motor/gearbox by adding or removing calibrated metal shims (sliders) under the pawls.
  6. Move the motor/gearbox horizontally using special tools to achieve acceptable misalignment values ​​(< 0.05 mm radially and angularly).
  7. Tighten the motor/reducer anchor bolts to the foundation to the torque specified by the manufacturer (eg M12: 80Nm, M16: 160Nm).
  8. Recheck alignment after tightening, as tightening may cause slight changes.
  9. Connect the clutch, check its condition.
  10. VERIFICATION: Run the equipment and repeat the vibration analysis and thermography. The vibration level should decrease significantly, and the temperature should normalize.

8.2. Replacement of bearings

  1. ⚠ SECURITY: Follow the LOTO procedure. Drain the grease (if disassembly is provided).
  2. Dismantle the gearbox from the equipment if complete replacement of the bearings is not possible on site.
  3. Disassemble the gearbox housing following the manufacturer's instructions.
  4. ⚠ PROTECTION: Protect exposed surfaces from contamination.
  5. Press out the damaged bearings with a suitable puller. DO NOT USE IMPACT METHODS THAT MAY DAMAGE THE SHAFT OR LANDING PLACE.
  6. Thoroughly clean the bearing seats on the shaft and in the housing. Check them for the absence of damage, burrs, production.
  7. Heat the new bearings to a temperature of 80-100°C (eg in an induction heater or oil bath) to facilitate seating on the shaft. DO NOT OVERHEAT!
  8. Install the bearings onto the shafts using special mounting tools or a hydraulic press.
  9. Assemble the gearbox, observing the tightening torques for the housing bolts (eg M10: 50 Nm, M14: 120 Nm) and adjusting the clearances.
  10. Fill in fresh lubricant of the type and volume recommended by the manufacturer (chapter 8.4).
  11. VERIFICATION: Start the equipment. Monitor the noise, vibration and temperature of the bearings. The temperature should stabilize within a few hours of operation.

8.3. Gear Repair/Replacement and Backlash Adjustment

  1. ⚠ SECURITY: Follow the LOTO procedure. Drain the oil.
  2. Dismantle the gearbox and disassemble its housing.
  3. Perform a visual inspection of all gears. Replace damaged (with chips, significant pitting, cracks) or excessively worn gears.
  4. Clean all components from old lubricants and dirt.
  5. When replacing gears, make sure that spare parts are used that meet the manufacturer's specifications (material, accuracy class, heat treatment). Spare parts certified by UkrSEPRO are recommended.
  6. Install new gears and adjust the side gap (backlash) between the teeth. Use a watch-type indicator and/or dipstick. The gap should be within the limits specified by the manufacturer (for example, 0.10-0.20 mm). Adjustment can be carried out with the help of spacers or displacement of the bearing units.
  7. Apply a thin layer of marker paint to the surface of the teeth to check the contact spot. Rotate the gear by hand and assess the location and size of the contact patch. It should be symmetrical and cover 70-80% of the length of the tooth.
  8. Assemble the gearbox by tightening all fasteners to the recommended torque.
  9. Add fresh oil.
  10. VERIFICATION: Run the gearbox at idle, then gradually under load. Control noise, vibration and temperature. Perform a vibration analysis to confirm the absence of peaks at the GMF.

8.4. Restoration of the lubrication system

  1. ⚠ SECURITY: Follow the LOTO procedure.
  2. Completely drain the old grease from the gearbox.
  3. Flush the internal cavities of the gearbox with a special flushing grease or a recommended solvent if the grease is heavily contaminated or degraded. Follow the detergent manufacturer's instructions.
  4. Replace all oil filters and oil seals if damaged or leaking.
  5. Fill with fresh grease, the type and viscosity of which fully correspond to the specifications of the gearbox manufacturer and the operating conditions (eg ISO VG 220 for moderate loads, ISO VG 320 for heavy loads). Use lubricants that meet the DSTU ISO 3448 standard.
  6. Check the oil level using a dipstick or sight glass. The level should be between the minimum and maximum marks.
  7. VERIFICATION: Start the reducer. Check the temperature, make sure there are no leaks. After 50-100 hours of operation, it is recommended to take a sample of the lubricant for control analysis to confirm purity and absence of rapid degradation.

9. Precautions

The root cause Prevention strategy Monitoring method Recommended interval
Misalignment of the shafts Accurate alignment of shafts during installation and after repair. Use of flexible couplings. Periodic vibration analysis, alignment measurement. Every 6-12 months or after any intervention.
Bearing wear Use of quality bearings (accuracy class according to ISO 492). Correct lubrication, adherence to lubrication schedules. Load control. Vibration analysis, acoustic control, thermography, lubricant analysis. Vibration: monthly; Oil analysis: every 6 months; Thermography: quarterly.
Gear wear Using the correct type and quality of lubricant. Load control. Adherence to the side clearance during assembly. Vibration analysis (GMF), lubrication analysis, periodic visual inspection (through a borescope). Vibration: monthly; Oil analysis: every 6 months; Boroscope: annually.
Oil problems Adherence to oil and filter replacement schedules. Use of lubricant recommended by the manufacturer. Control of cleanliness and tightness of the system. Lubricant analysis, visual control of the level and condition of the lubricant, thermography. Oil analysis: every 3-6 months; Visual control: weekly.
Loose fasteners Use of thread lock (for example, Loctite). Regular control of tightening moments. Visual inspection, thermography (local heating), vibration analysis. Quarterly.

10. Spare parts and components

Timely replacement of worn components is critical for the longevity of the gearbox. Pay attention to the quality and compliance of components with standards (for example, bearings according to ISO, seals according to EN). All spare parts must have appropriate quality certificates, including UkrSEPRO for the Ukrainian market.

Description of the part Specification When to replace Category UNITEC
Ball/roller bearings According to the manufacturer's marking (eg 6205 2RS C3, 22220 KMB), accuracy class P6/P5 (ISO). When wear, pitting, local overheating is detected, or after the service life has expired (usually 20,000-50,000 hours). Bearings
Gear set Module, number of teeth, material (for example, 20CrMnTi), accuracy class for DIN 3961/62. In case of significant wear of teeth (more than 20% of the thickness), chips, cracks, or when the side clearance exceeds 50% of the norm. Transmission components
Oil seals/Shaft seals Size (eg 40x60x10), material (NBR, FKM/Viton), type (single/double edge). When detecting lubricant leaks, hardening, mechanical damage. Sealing
Body gaskets Material (asbestos-free paronite, rubber), thickness, shape. When disassembling the gearbox for repair, or when leaks are detected. Sealing
Lubricant for gearboxes Type (mineral, synthetic), viscosity (ISO VG 220, 320, 460), EP class (eg CLP). According to the service schedule (for example, every 1500-3000 hours of operation), or according to the results of the analysis of the lubricant. Lubricating materials
Oil filter Degree of filtration (micron), size, type. According to the maintenance schedule, or according to the results of the analysis of the lubricant (high content of particles). Filter elements

All necessary spare parts and lubricants that meet international standards and have the necessary certificates are available in the UNITEC-D electronic catalog: https://www.unitecd.com/e-catalog/

11. Links

  • DSTU ISO 10816-1:2003: Vibration. Evaluation of machine vibration based on the results of measurements on non-rotating parts.
  • DSTU ISO 2909:2009: Oil and oil products. Calculation of viscosity index by kinematic viscosity.
  • DSTU ISO 3104:2008: Oil products. Transparent and opaque liquids. Determination of kinematic viscosity and calculation of dynamic viscosity.
  • DSTU ISO 3448:2009: Industrial liquid lubricants. ISO viscosity classification.
  • ISO 4406:1999: Hydraulic power transmission. liquids The method of coding the level of pollution by solid particles.
  • ISO 492:2014: Roller bearings. Radial bearings. Tolerances
  • Original manuals for operation and maintenance of gearboxes UNITEC-D GmbH.
  • UNITEC-D Guides: https://www.unitecd.com/maintenance-guides/

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