Gearbox Maintenance: Oil Change, Checking Gears, Seals and Alignment
1. Scope and Purpose
This manual covers scheduled maintenance procedures for industrial gearboxes, including changing the transmission oil, visual and instrumental inspection of the condition of the gears, shaft seals, and checking and adjusting the alignment of the gearbox shafts with the drive and driven mechanisms. Applies to most standard cylindrical, bevel and worm gears used in the metallurgical, chemical, food and energy industries. Carrying out these works is critical for ensuring long-term and reliable operation of the equipment, preventing emergency failures and optimizing operating costs. Maintenance should be performed in accordance with the equipment manufacturer's (OEM) recommendations or in accordance with the preventive maintenance schedule, but no less often than once every 12 months or after every 2000 hours of operation.
2. Security measures
WARNING! Before starting any work on the gearbox, be sure to read the equipment manufacturer's instruction manual and follow all corporate safety procedures. Failure to follow these instructions could result in serious personal injury or equipment damage.
ATTENTION! Lockout and Tagout (LOTO): Before disassembling or servicing the reducer, be sure to perform a full Lockout/Tagout procedure on all power sources (electrical, hydraulic, pneumatic, mechanical) powering the drive mechanism. Make sure that the mechanism cannot be started unexpectedly. Comply with DSTU standards ISO 14118.
ATTENTION! Personal Protective Equipment (PPE): When working with the reducer, use appropriate PPE: safety glasses or shield, gloves (chemically resistant when working with oil), protective clothing, protective shoes. When working in a confined space or with an increased noise level, use ear protection.
ATTENTION! Hot Oil and Surfaces: Transmission oil and gear parts may be hot after operation. Allow equipment to cool to a safe temperature (<50°C) before draining oil or touching surfaces. Use a thermometer to check the temperature.
ATTENTION! Lifting Heavy Objects: Gears and their components can be heavy. Use proper lifting equipment and safe lifting techniques to avoid back injuries.
ATTENTION! Waste Disposal: Used oil is a hazardous waste. Collect it in special hermetic containers and dispose of it in accordance with environmental regulations and rules. Follow the norms of DSTU 4462.3.01:2006.
3. Necessary Tools and Materials
| Name of Tool/Material | Specification | Quantity |
|---|---|---|
| A set of wrenches | Sizes from 10 mm to 36 mm | 1 set |
| Torque wrench | Range 20-200 Nm, step 1 Nm, accuracy class ±4% | 1 pc. |
| Screwdrivers | Flat and cross-shaped (PH1, PH2), different sizes | 1 set |
| Container for collecting used oil | A capacity that exceeds the oil volume in the gearbox by 25% (for example, 25 L for a 20 L gearbox) | 1 pc. |
| Vomit | With mesh filter | 1 pc. |
| New transmission oil | According to the gearbox manufacturer's specification (eg ISO VG 220, ISO VG 320), API class GL-4 or GL-5 | Required volume + 10% margin |
| Industrial rags | Hairless | 1 package |
| Cleaner for metal | Non-flammable, residue-free (e.g. isopropyl alcohol) | 1 balloon |
| Sealant for threaded connections | Medium strength (e.g. Loctite 243) | 1 tube |
| Manometer | Range 0-10 bar, accuracy class 1.0 | 1 pc. (if there is a pressure control point) |
| Infrared thermometer | Range -30°C to +400°C | 1 pc. |
| A set of probes | Range 0.02 - 1.00 mm, step 0.01 mm | 1 set |
| Caliper for checking tooth wear | Depends on the gear module | 1 set (as needed) |
| Laser shaft alignment system | Accuracy ±0.01 mm/m | 1 set |
| Clock-type indicator with a stand | Accuracy 0.001 mm | 1 pc. |
| A set of seals and oil seals | Original spare parts or analogs that meet the specifications of the gearbox manufacturer | 1 set (according to the spare parts list) |
| Syringe for oil sampling | The volume is 50-100 ml | 1 pc. |
| Tag for used oil | With gear and date information | 10 pcs. |
| Wooden or rubber mallets | Different sizes | 1 set |
| Safety glasses | According to EN 166 | 1 pair |
| Protective gloves | Chemically resistant (nitrile or neoprene) | 1 pair |
4. Pre-Service Checklist
| Element | Verification | Acceptance/Rejection Criteria | Notes |
|---|---|---|---|
| General condition of the gearbox housing | Visual inspection for cracks, deformations, corrosion | No visible damage | Record any defects |
| Oil level | Visual inspection through a level indicator or dipstick measurement | Within the minimum and maximum levels | If the level is low, record a possible leak. |
| Oil color and transparency | Visual inspection of the oil sample | Transparent, without impurities, typical color for new oil. Absence of turbidity, water, metal particles. | Record any anomalies. |
| The smell of oil | Evaluation of the smell of the oil sample | Absence of sharp, burning smell | A pungent odor may indicate overheating or oxidation. |
| Gearbox temperature | Measurement with an infrared thermometer on the body | The body temperature does not exceed 70°C at nominal load | High temperature indicates excessive friction or insufficient cooling. |
| Noise and vibration | Listening, tactile inspection, measurement with a vibrometer (if available) | Absence of uncharacteristic noises (knocking, grinding), vibration within the OEM norm | Any abnormalities indicate worn bearings or gears. |
| Hermeticity of seals | Visual inspection around shafts, plugs, flanges | Absence of visible oil leaks, drips, fogging | Leaks require replacement of seals. |
| Condition of the ventilation hole (soap) | Visual inspection | Clean, not clogged with dirt, free passage of air | A clogged breather can lead to increased pressure inside the reducer and leaks. |
| The condition of the foundation and fastening | Visual inspection, checking the tightness of the fastening bolts | Reliable fastening, absence of backlash, cracks in the foundation | A loose mount can cause vibration and misalignment. |
| Availability of protective covers | Visual control | All guards are in place and securely fastened | The absence of covers is a violation of safety technology. |
5. Step-by-step Procedure
5.1. Preparation
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Stopping the equipment and blocking the power source.
Before starting any work, make sure that the gearbox is completely stopped.
CAUTION! Perform a Lockout and Tagout (LOTO) procedure in accordance with DSTU standards ISO 14118. Place a DO NOT TURN ON! WORK IS GOING ON!".
Error: Failure to perform LOTO is a serious safety violation and may result in fatal injury. -
Cleaning the outer surfaces of the gearbox.
Use metal cleaner and industrial rags to remove dirt, dust, oil residue from the gear housing. This prevents dirt from getting inside when opening the covers or draining the oil.
Visual indicator: Clean external surfaces without dirt and dust.
Error: Dirt can enter the system when draining/filling oil. -
Preparation of tools and containers.
Lay out all necessary tools and materials in accordance with Section 3. Place a clean container to collect the used oil directly below the gearbox drain. Make sure that the container is of sufficient volume.
Visual indicator: All tools are at hand, the oil container is ready.
5.2. Draining Used Oil
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Oil sampling (for analysis, if required).
If an oil condition analysis is planned, use a sampling syringe to take about 50-100 ml of used oil from the drain hole or through the filler hole. Label the sample with the date and gear ID.
Error: Untimely sampling may not reflect the actual condition of the oil during operation. -
Opening the drain hole.
Carefully unscrew the gearbox drain plug using the appropriate wrench. Allow the oil to drain completely into the prepared container. This usually takes 15-30 minutes, depending on the viscosity of the oil and the temperature. To speed up the drain, you can open the filling hole and breather for air access.
Visual indicator: The oil has completely glassed, the flow has stopped or has become very slow.
Error: Incomplete drain leaves old oil, reducing replacement efficiency. Overview of drain plug and magnetic trap.
If the drain plug has a magnetic trap, carefully inspect it for metal particles. Small fine particles are normal, but large amounts of chips or metal fragments (larger than 1 mm) indicate significant gear or bearing wear.
Visual indicator: The magnetic trap is clean or contains a minimal amount of fine particles.
Bug: Ignoring a large amount of metal can lead to catastrophic gear failure.-
Cleaning and installing the drain plug.
Thoroughly clean the drain plug and its thread from old sealant and dirt. Replace the O-ring (if provided) with a new one. Apply a new thread sealant (such as Loctite 243) to the threads of the drain plug. Install the plug and tighten it with a torque wrench to the torque recommended by the manufacturer (usually 30-50 Nm for M20-M24 plugs).
Visual indicator: The plug is tightly tightened, with no signs of leakage.
Error: Undertightening will lead to leakage, overtightening will damage the thread or plug.
5.3. Inspection of Gears and Internal Components
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Opening inspection hatches/covers.
Unscrew the bolts securing the inspection hatches or the top cover of the gearbox.
CAUTION! Be careful not to damage the gaskets or seals. If necessary, gently lift the cover with a wooden or rubber mallet.
Bug: Using metal dressing tools can damage the mating surfaces, causing leakage. -
Visual inspection of gears.
Carefully inspect all available gears for the following defects: pitting, tooth chips, tooth wear (profile), cracks, excessive polishing (mirror wear), signs of corrosion. Use a light source and a magnifying glass. Record any defects.
Criteria: No chips, cracks. Pitting is permissible on 10% of the tooth area. The wear of the profile is no more than 0.1 mm from the initial one.
Flaw: Ignoring the initial stages of wear will lead to rapid progression of the defect and failure. -
Checking the condition of the bearings (if available).
If possible, inspect the bearing spacers and rollers/balls. Turn the shafts by hand, listen for extraneous noises (creaking, backlash).
Criteria: Smooth movement, no backlash and extraneous noise.
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Cleaning of internal surfaces.
Remove old oil and dirt from the inside walls of the housing and gears. Use clean, lint-free cloths and metal cleaner. Avoid getting the cleaner on the seals unless they will be replaced.
Error: Residues of old oil and dirt will contaminate the new oil. -
Closing inspection hatches/covers.
Install new gaskets or apply a thin layer of sealant (if recommended by the OEM) to the bearing surfaces. Install the covers and evenly tighten the mounting bolts with a torque wrench. The tightening torque depends on the diameter of the bolts (for example, for M10 45-50 Nm, for M12 75-80 Nm). Tighten "cross-cross".
Visual indicator: Caps fit tightly, bolts are tightened evenly.
Error: Uneven tightening can deform the cap or cause leakage.
5.4. Replacement of Seals (Glands)
Replacement of seals is recommended when leaks are detected or during major repairs. If the seals are dry and do not show signs of leakage, they can be left unchanged, but their condition should be monitored.
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Dismantling of shaft seals.
Carefully remove the old oil seals (shaft seals) using a special puller or screwdriver, prying them from the inner edge.
CAUTION! Do not damage the seats and surfaces of the shafts!
Error: Damage to the shaft or housing will prevent a hermetic installation of a new seal. -
Cleaning and inspection of seats.
Thoroughly clean the seal seat from dirt, old sealant and oil. Inspect the shaft surface on which the seal works for burrs, deep scratches, or wear. Minor scratches can be polished with fine sandpaper (P2000) with oil.
Error: The presence of defects on the shaft will lead to rapid wear of the new seal and leaks. -
Installing new seals.
Lubricate the working edge of the new seal with clean gear oil. With the help of a special mandrel (or a piece of pipe of the appropriate diameter), carefully, evenly, without distortions, press the new seal into the seat until it stops. Make sure the seal spring is on the oil side.
Visual indicator: The seal is installed flat, without distortion, the working edge is not damaged.
Error: A misalignment of the seal or damage to the working edge will lead to leakage.
5.5. Pouring Novy Masla
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Filling oil.
Using a clean strainer, slowly add new transmission oil through the filler hole until the recommended level is reached on the dipstick or dipstick. The oil volume must comply with the gearbox manufacturer's specifications.
Visual indicator: The oil level is between the minimum and maximum marks.
Error: Overfilling oil can lead to foaming and overheating, underfilling - to oil starvation and accelerated wear. -
Filling plug and breather.
Clean the filler cap and breather. Replace the sealing rings. Tighten the filler plug with a torque wrench (as for the drain plug). Install the breather, making sure it is clean and working.
Visual indicator: Plugs are tight, breather is clean.
5.6. Inspection and Adjustment of Shaft Alignment
This procedure is critical to prevent excessive vibration, bearing and seal wear, and coupling damage.
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Preparation for alignment measurement.
Make sure the gearbox and drive/driven mechanisms are securely fastened. Clean the surfaces of shafts and couplings.
CAUTION! Ensure equipment is de-energized and locked out (LOTO). -
Alignment measurement (laser system).
Install the laser alignment system sensors on the gearbox and drive/driven shafts according to the system manufacturer's instructions. Measure axial and angular displacement.
Criteria: Allowable axial displacement no more than 0.05 mm, angular displacement no more than 0.02 mm/100 mm of shaft length.
Error: Excessive displacement will lead to accelerated wear of couplings, bearings and vibration. -
Alignment adjustment.
If the alignment is not correct, use shims under the legs of the gear and/or drive mechanism to adjust the axial and angular misalignment. Adjust the vertical and then the horizontal alignment successively, repeating the measurement after each change until acceptable values are reached.
Visual indicator: The laser system reading indicates "PASS" or is in the green tolerance range.
Error: Uneven tightening of the bolts after adjustment may again disturb the alignment. -
Tightening the fastening bolts.
After achieving the required alignment, tighten all the fixing bolts of the gearbox to the recommended torque with a torque wrench (for example, for M16 bolts of strength class 8.8 - 200 Nm, for M20 - 390 Nm). Recheck alignment after tightening.
Visual indicator: Alignment preserved after tightening.
6. After-Service Checklist
| Test | Expected Result | Actual Result | Pass/Fail |
|---|---|---|---|
| Oil level | Within the normal range (between the minimum and maximum marks) | ||
| No leaks | Absence of oil drips around plugs, seals, covers | ||
| Oil color and transparency | Clean, transparent, matching color | ||
| The temperature of the gearbox housing | Stable, does not exceed 70°C after 1 hour of work under load | ||
| Normal level of noise and vibration | Absence of unusual noises and vibrations | ||
| Correctness of shaft alignment | Axial and angular misalignment within OEM tolerances (<0.05 mm axial, <0.02 mm/100 mm angular) | ||
| Availability and integrity of protective covers | All covers are in place, securely fastened | ||
| Clean workplace | The area around the equipment is clean, without tools and materials | ||
| Unblocking (LOTO) | The LOTO lock is removed after confirming that the equipment is ready for operation |
7. Troubleshooting Guide
| Symptom | Probable Cause | Corrective Action |
|---|---|---|
| High gear temperature (>80°C) | Low oil level; excessive load; worn bearings or gears; wrong type of oil; oil contamination; clogged breather. | Check the oil level and top up; reduce the load; carry out diagnostics of bearings/wheels; replace the oil with the appropriate one; replace the oil; clean the breather. |
| Excessive noise (knock, screeching) | Gear wear; bearing wear; incorrect alignment; low oil level; mechanical damage. | Carry out a detailed inspection of the gears; replace bearings; check and adjust alignment; check the oil level; carry out diagnostics for mechanical damage. |
| Oil leakage due to shaft seals | Wear or damage to the oil seal; shaft surface damage; excessive pressure inside the reducer (clogged breather); incorrect installation of the oil seal. | Replace the oil seal; polish or replace the shaft; clean the breather; reinstall the oil seal in accordance with the technology. |
| Oil leakage through cover gaskets | Damage to the gasket; loose fastening bolts; deformation of the cover. | Replace the gasket; tighten the bolts to the recommended moment; align or replace the cover. |
| Strong vibration of the gearbox | Clutch imbalance; incorrect alignment of the shafts; weakened attachment to the foundation; bearing wear; gear damage. | Balance the clutch; align the shafts; tighten fasteners; replace bearings; inspect the gears. |
| The oil quickly gets dirty/blackened | Oil overheating; oil oxidation; ingress of external pollution; gear wear (metal shavings). | Check the causes of overheating; replace the oil and ensure proper cooling; check the tightness of the breather and seals; inspect internal components. |
8. Recommended Maintenance Schedule
The schedule is based on typical operating conditions. In conditions of increased loads, high temperatures or a polluted environment, the frequency of maintenance should be increased.
| Task | Frequency | Estimated time (hours) | Qualification Level |
|---|---|---|---|
| Checking the oil level | Weekly | 0.1 | Operator / Technician |
| Visual inspection of the sources | Weekly | 0.1 | Operator / Technician |
| An overview of soap | Monthly | 0.1 | Technician |
| Sampling of oil for analysis | Quarterly / Every 500 hours | 0.5 | Technician / Reliability Engineer |
| Transmission oil replacement | Annually / Every 2000-4000 hours | 2-4 | Technician |
| Checking the condition of gears and bearings (through the inspection hatch) | Annually / Every 2000-4000 hours | 1-2 | Technician |
| Checking and adjusting shaft alignment | Annually / Every 2000-4000 hours | 2-3 | Technician / Reliability Engineer |
| Replacement of seals (seals) | As needed or every 3-5 years | 2-4 | Technician |
| Overhaul of the gearbox | Every 5-10 years / Every 20,000-40,000 hours | 40-80 | Specialist / Service team |
9. Catalog of Spare Parts
The use of high-quality spare parts is a guarantee of reliable operation of the gearbox. It is recommended to use original spare parts or certified analogues that meet ISO and EN standards.
| Description Details | Typical Specification | Category UNITEC |
|---|---|---|
| Transmission oil | ISO VG 220, ISO VG 320, GL-4/GL-5 | Lubricating materials |
| Shaft seal (seal) | NBR, FKM (according to temperature), size according to OEM (eg 85x110x12) | Sealing |
| Cover gasket | Asbestos-free, thickness 0.5-1.0 mm, material (for example, reinforced paronite) | Sealing |
| Vent (soap) | Thread M16x1.5, M20x1.5, filter 10 μm | Accessories for reducers |
| Bearings | Ball-radial, roller-conical/spherical (according to OEM), accuracy class P0/P6 | Bearings |
| Fastening bolts | Strength class 8.8, 10.9 (DIN 931/933), nuts DIN 934 | Fastening |
| Sealant for threaded connections | Anaerobic, medium strength (e.g. Loctite 243) | Sealants and sealants |
| Drain/fill plug | Thread M20x1.5, M24x1.5, material steel/brass | Accessories for reducers |
| Oil level indicator | Thread G 1/2", G 3/4", material polyamide/brass | Accessories for reducers |
To order high-quality spare parts and components, visit the electronic catalog UNITEC-D.
10. Links
- DSTU EN ISO 12100:2016 - Machine safety. General design principles. Risk assessment and risk reduction.
- DSTU ISO 14118:2009 — Machine safety. Prevention of unexpected start.
- DSTU 4462.3.01:2006 — Environmental protection. Waste management. Waste classification procedure.
- DSTU ISO 2954:2018 — Mechanical vibration. Measurement and evaluation of machine vibration.
- Gearbox Manufacturer's (OEM) Operation and Maintenance Manual.
- DIN standards ISO 281, ISO 15243 (for bearings).
- Standards ANSI/AGMA 2000-A88, DIN 3990 (for gears).
