Lubricating Oil Oxidation Stability Tester (Rotating Oxygen Bomb Method) – ASTM D2272
The Rotating Oxygen Bomb (ROB) Test, also known as ASTM D2272, is a widely used method to evaluate the oxidation stability of lubricating oils by measuring the time it takes for oil to react with oxygen under accelerated conditions. This test is essential for turbine oils, hydraulic oils, and other high-performance lubricants.
1. Equipment & Materials Needed
A. Instrumentation
✅ Rotating Oxygen Bomb Tester – Must have:
- Stainless steel oxygen bomb
- Rotating sample holder (100 rpm)
- Constant temperature oil bath (150°C ± 0.1°C)
- Pressure transducer & data logger
✅ Oxygen Supply System
- 99.5% pure oxygen (O₂)
- High-pressure oxygen regulator
B. Reagents & Consumables
✅ Copper Catalyst Coil – 99.99% pure copper, pre-cleaned
✅ Distilled Water – Used for moisture content control
✅ Lubricating Oil Sample – Typically 50 mL per test
✅ Reference Oil Standard – For instrument calibration
2. Testing Procedure (ASTM D2272)
A. Sample Preparation
1️⃣ Clean & Dry the Bomb:
- Wash with solvent, then dry with compressed air.
- Ensure no contamination inside.
2️⃣ Prepare the Copper Catalyst:
- Use a new or properly cleaned copper coil.
- If reusing, clean with solvent + ultrasonic bath, then dry.
3️⃣ Measure & Load the Sample:
- Pour 50.0 mL of lubricant into the bomb.
- Add 5 mL distilled water for controlled reaction.
- Insert the copper catalyst coil into the bomb.
B. Test Execution
4️⃣ Seal the Bomb & Purge with Oxygen:
- Close the bomb tightly and fill with 99.5% pure oxygen to 620 kPa (90 psi).
- Hold for 1–2 minutes to allow oxygen saturation.
5️⃣ Start the Rotating Bomb Test:
- Place the bomb in the oil bath at 150°C.
- Rotate at 100 rpm continuously.
6️⃣ Monitor Pressure Drop:
- As oxidation progresses, oxygen reacts with oil, causing a pressure drop.
- The end of the test is when pressure drops by 25 psi (172 kPa).
C. Data Analysis & Interpretation
✅ Oxidation Stability Time (minutes)
- The time from test start until pressure drops by 25 psi is recorded.
- Longer time → Better oxidation stability.
✅ Typical Results for Different Oils
| Oil Type | Oxidation Stability (minutes) |
|---|---|
| Turbine Oil (ISO 32/46/68) | 800–1600 min |
| Hydraulic Oil | 400–1200 min |
| Compressor Oil | 500–1500 min |
| Synthetic Lubricants | >2000 min |
🔹 High-performance oils have longer oxidation stability times due to antioxidant additives.
3. Factors Affecting Oxidation Stability
| Factor | Effect |
|---|---|
| Base Oil Type | Synthetic oils resist oxidation better than mineral oils |
| Additives (Antioxidants) | Increase oxidation resistance significantly |
| Contaminants (Water, Metals) | Reduce oxidation stability |
| Operating Temperature | Higher temperature accelerates oxidation |
4. Equipment Calibration & Quality Control
✅ Calibration with Standard Oils:
- Run reference oils with known oxidation stability.
- Compare results to ensure accuracy.
✅ Duplicate Testing:
- Run duplicate tests on the same sample (variation <5%).
✅ Oxygen Purity Check:
- Impurities in oxygen can affect results. Use >99.5% pure O₂.
5. Troubleshooting & Common Issues
| Issue | Possible Cause | Solution |
|---|---|---|
| Short oxidation time | Contaminated sample | Use fresh oil, clean test equipment |
| Irregular pressure drop | Leaking bomb seal | Tighten seal, check gaskets |
| Excessive pressure drop | Water contamination | Dry oil sample before testing |
| No reaction detected | Faulty pressure sensor | Check instrument calibration |
6. Advantages of the Rotating Oxygen Bomb Method
✔ Rapid Test – Results in 2–10 hours instead of weeks/months.
✔ High Sensitivity – Detects oxidation early before viscosity changes.
✔ Widely Accepted – Standardized by ASTM D2272, ISO 7536, IP 229.
✔ Predictive Maintenance – Helps in oil selection & replacement schedules.
7. Conclusion & Recommendations
- ASTM D2272 (Rotating Oxygen Bomb Test) is ideal for evaluating oxidation resistance in turbine oils, hydraulic oils, and synthetic lubricants.
- Longer oxidation times indicate better lubricant quality and stronger antioxidant protection.
- Regular testing helps extend oil life, prevent varnish formation, and optimize maintenance schedules.