SH/T 0325-1992 Determination of Oxidation Stability of Lubricating Grease

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: SH/T 0325-92 (confirmed in 2004)
• Chinese name: Determination of Oxidation Stability of Lubricating Grease
• English name: not provided in the available source
• Replacement relationship: replaces ZB E36 022—89
• Reference adoption: ASTM D942-78 (84) "Determination of Oxidation Stability of Lubricating Grease"
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• Applicable: determination of the oxidation stability of lubricating grease by the oxygen bomb method; applicable to determining the oxidation resistance of lubricating grease statically stored in a closed oxygen system under conditions of elevated test temperature; can be used for quality control to indicate batch stability.
• Not applicable/does not predict: does not predict the stability of lubricating grease under dynamic working conditions and the stability of lubricating grease during long-term storage in containers, nor does it predict the stability of thin layers of lubricating grease on bearings and motor parts; shall not be used to evaluate the relative oxidation resistance of different types of lubricating grease.

3. Method principle

Place the sample in an oxygen bomb heated to 99°C and filled with 758kPa oxygen for oxidation. Observe and record the pressure at specified time intervals. After a specified time period, determine the degree of oxidation of the lubricating grease from the corresponding decrease in oxygen pressure.

4. Reagents and materials (purity / preparation)

• 3.1 Reagents
  • Petroleum ether: 90~120°C, analytical reagent; or solvent naphtha for the rubber industry.
• 3.2 Materials
  • Oxygen: purity not less than 99.5%.

5. Apparatus and equipment

• 4.1 Oxygen bomb, sample dishes, dish rack, pressure gauge and oil bath, see Appendix A for detailed description.
  • Note: If the heat capacity and thermal gradient characteristics are comparable to the oil bath described in the appendix and the oxygen bomb can be maintained at the specified test temperature, other constant-temperature baths may also be used.
• 4.2 Thermometer: temperature range 95~103°C, scale division value 0.1°C, see Appendix B.
• Appendix A (supplementary document) Apparatus:
  • A1 Oxygen bomb: made of alloy steel with 18% chromium and 8% nickel; at 99°C it shall be able to safely withstand a working pressure of 1241kPa; equipped with lead or polytetrafluoroethylene gasket seals; the inner walls of the lid and the pressure gauge conduit shall be highly polished; the volume of the oxygen bomb without the dish rack and dishes (measured to the height of the pressure gauge) shall be 185mL±6mL; a screw cap may be used instead of a bolt-fixed lid.
  • A2 Pressure gauge: an indicating pressure gauge suitable for oxygen and mineral oil, with a scale interval of 6.89kPa per division, a maximum reading of at least 827kPa, and an accuracy of at least 3.45kPa within the range 621~827kPa; a recording pressure gauge may be used instead.
  • A3 Oil bath: capable of being controlled at 99°C±0.5°C, the temperature change rate of the oil bath used shall be less than 0.5°C; shall have sufficient depth to immerse the oxygen bomb to an appropriate depth; it is recommended to use a pump or stirring to circulate the heating medium oil; shall have sufficient heat capacity to bring the oil bath to the required temperature within 60min after the oxygen bomb is immersed; have a thermometer insertion hole so that the thermometer 96.8°C position is at the same level as the upper surface of the oil bath lid; adjust the bath surface so that the top of the oxygen bomb is immersed about 50mm below the oil surface; shall be placed in a place free from drafts or large fluctuations in temperature around the pressure gauge.
  • A4 Dish rack: made of alloy steel with 18% chromium and 8% nickel, the same material as the oxygen bomb, conforming to the dimensions specified in Figure A1.
  • A5 Glass sample dish: conforming to the dimensions specified in Figure A1.
• Appendix B (supplementary document) Thermometer specifications:
  • Range: 95~103°C
  • Test temperature: 98.9°C
  • Immersion depth: total immersion
  • Scale division value: 0.1°C
  • Long-line scale value: 0.5°C
  • Per graduation: 0.1°C
  • Scale error (maximum): not provided in the available source (source-text extraction doubtful point, requires confirmation against the source standard)
  • Expansion chamber permitted to be heated to: 155°C
  • Total length: 270~280mm
  • Stem diameter: 6.0~8.0mm
  • Mercury bulb length: 25~35mm
  • Mercury bulb diameter: ≥5.0mm and ≤ stem diameter
  • Scale positioning: 95°
  • Distance from bulb bottom to graduation line: 135~150mm
  • Length of graduated portion: 70~100mm
  • Distance from bulb bottom to bottom of contraction chamber (minimum): 60mm
  • Distance from bulb bottom to top of contraction chamber (maximum): not provided in the available source (source-text extraction doubtful point, requires confirmation against the source standard)
  • Enlarged portion of stem: diameter 8.0–10.0mm; length 4.0–7.0mm; distance to bottom 112~116mm

6. Recommended operating conditions

• Oxidation temperature: 99°C (oil bath maintained at 99°C±0.5°C)
• Oxygen pressure: 758kPa±14kPa
• Pressure observation and recording interval: observe and record at least once every 24h
• Test time: continuous oxidation until the time period specified in the product specification (the product specification usually gives a pressure drop (kPa) period with one or more time intervals, such as 100, 200h, etc.)

7. Sampling and sample preparation

• 6.1 Place 4.00g±0.01g sample in each of 5 dishes. Distribute the sample evenly in the dish, and its upper surface shall be smooth. Place the dishes containing the samples on the 5 bottom shelves of the dish rack respectively. Leave the top shelf as a cover to prevent condensed volatiles from dripping into the sample. When assembling the oxygen bomb, place a small wad of glass wool in the opening at the bottom of the tube connecting to the pressure gauge.
  • Note: If a balance with a scale division value of 0.01g is not available, a balance with a scale division value of 0.1g may also be used for weighing, but for arbitration tests a balance with a scale division value of 0.01g must be used for weighing.

8. Analytical procedure

• 5 Apparatus preparation
  • 5.1 Clean all dirt from the previous test and dust deposits from the air in the sample dishes, washing successively with solvent, hot detergent water and hot chromic acid cleaning solution. Finally rinse thoroughly with tap water, then rinse with distilled water, and place in an oven to dry. Cleaned dishes shall only be handled with tweezers.
  • 5.2 If after the test a varnish film is found on the oxygen bomb and metal dish rack, immerse them in hot solvent, scrub the interior with a stiff-bristle brush, then remove and dry. Further scrub with water and a fine scouring powder until all varnish deposits are removed. Finally rinse thoroughly with tap water and dry in an oven. Cleaned metal dish racks shall only be handled with tweezers.
• 6 Test procedure
  • 6.1 See Section 7 Sampling and sample preparation.
  • 6.2 Place the dish rack into the oxygen bomb, and slowly and evenly tighten the bolts to seal the oxygen bomb. Slowly introduce oxygen until the pressure reaches 689kPa, then slowly release the oxygen to expel the air in the oxygen bomb. Repeat 4 times, so that the oxygen pressure reaches the following values:

• Allow the oxygen bomb to stand overnight to check for leakage.
• Note: At the pressures indicated above, when the oxygen bomb is placed in the bath according to the procedure in 6.3, the pressure reading rises exactly to 758kPa±14kPa. Therefore, in most cases it is not necessary to release oxygen. In this case, for an oxygen bomb that has been proven to meet the requirements by the overnight leakage check, the chance of leakage at the valve can be minimized.
• 6.3 Place the oxygen bomb in an oil bath maintained at a temperature of 99°C±0.5°C; when the pressure rises above 758kPa±14kPa, intermittently release oxygen from the oxygen bomb until the pressure stabilizes at 758kPa±14kPa and remains so for at least 2h. If the pressure gradually decreases, it indicates that the oxygen bomb is continuously leaking. Observe and record the pressure at least once every 24h. In the event of leakage, do not report the results, but repeat the test.
• 6.4 Start timing immediately when the oxygen bomb is immersed in the oil bath, and continue oxidation until the time period specified in the product specification.
• Note: The product specification usually gives a pressure drop (kPa) period with one or more time intervals, such as 100, 200h, etc.

9. Qualitative and quantitative determination and calculation formula

• Determine the degree of oxidation of the lubricating grease from the corresponding decrease in oxygen pressure.
• Report the average of two results from duplicate determinations within the specified test time as the pressure drop (kPa) of the determination result.
• Calculation formula: not provided in the available source.

10. Precision

Judge the reliability of the test results according to the following provisions (95% confidence level).

7.1 Repeatability: The difference between two results of duplicate determinations by the same operator shall not be greater than the following values.

7.2 Reproducibility: The difference between two results submitted by different laboratories shall not be greater than the following values.

Note: These precision data are only applicable to the part of the data where the oxygen absorption rate is approximately proportional to time, before the induction period. A rapid acceleration of the oxygen absorption rate within a short time interval indicates that the induction period has been reached.

11. Report

Report the average of two results from duplicate determinations within the specified test time as the pressure drop (kPa) of the determination result.

12. Referenced documents

• ASTM D942-78 (84) "Determination of Oxidation Stability of Lubricating Grease" (reference adoption)
• Appendix A (supplementary document) Apparatus
• Appendix B (supplementary document) Thermometer specifications

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference Q&A