Is air harmful to lubricating oil?
The lubrication system is a critical component of various machinery and vehicles, with one of the key maintenance points being the prevention of impurities. We generally pay attention to contaminants such as dust, particulate matter, and moisture, often overlooking air.
Yes, air does indeed affect the performance of lubricating oil. Although it is unavoidable for lubricating oil to come into contact with air, the presence of air mixed into the oil, such as foam on the oil surface or bubbles trapped within the oil that cannot be released, can negatively impact lubrication. Generally, when lubricating oil is exposed to air, it undergoes slow oxidation (contact with oxygen), but this process is relatively gradual and is an unavoidable, normal occurrence. However, if air enters the interior of the lubricating oil, the problem becomes much more significant.
The air mixed in lubricating oil mainly consists of three types: air dissolved in the oil (invisible to the naked eye), bubbles suspended and trapped within the oil that cannot be released, and foam on the oil surface. Among these, the bubbles suspended and trapped within the oil pose the greatest harm to machinery and lubricating oil.
Foam tends to accumulate and float on the oil surface, with a relatively large volume. If foam appears, it generally indicates that bubbles may have already formed within the oil. Bubbles remain suspended and trapped inside the oil, smaller in size but highly detrimental. Bubbles can cause the oil to appear cloudy. If the oil is turbid, a sample can be taken; if stratification occurs, the cloudiness is likely due to contamination by water or other liquids. If the sample clears after standing for a while, it indicates the presence of air bubbles mixed into the oil.
Reasons for bubbles in lubricating oil:
Many factors can cause an increase in bubbles and foam in lubricating oil, with one common reason being the ingress of water. When water mixes into the oil, the surface tension of the oil decreases, preventing the formation of large bubbles that would float to the surface. Instead, they break into tiny bubbles suspended within the oil.
Lubricating oil is contaminated: other liquids, cleaning agents, solvents, etc., are mixed into the oil.
Lubricating oil oxidation: The oxidation of oil leads to a decrease in its anti-foaming properties. Some oils may exhibit increased foaming after prolonged use, with the common cause being oil oxidation.
Additive Depletion: The depletion of defoamers can also lead to increased foam formation. It's important to note that excessive addition of defoamers can also cause foam issues. Some users, upon noticing increased foam or depletion of defoamers, may add more defoamers, but over-adding can similarly result in foam problems.
Leakage: Air leakage at oil pipes, seals, and other parts.
Poor fuel tank design: The tank is too small, lacks bubble-filtering screens or baffles, the return and suction pipes are too close together, and the oil flow rate is too fast to allow for bubble release.
The viscosity of the lubricating oil is improperly selected.
The hazards of bubbles and foam in lubricating oil:
Bubbles and foam are harmful to both lubricating oil and machinery. Bubbles accelerate the oxidation and degradation of the oil, hasten the depletion of additives, impair heat dissipation, prevent the formation of a complete lubricating oil film, and cause wear on equipment. In high-pressure systems, bubbles can also lead to localized high temperatures, rapidly deteriorating the oil.
Hazards to the equipment:
Air is easy to compress, and if there is gas in the lubricating oil, the oil film thickness will become thinner or even rupture, leading to direct friction between mechanical parts and causing wear.
Causing cavitation: Bubbles collapse under pressure, leading to cavitation damage on metal surfaces.
Affecting mechanical operation: Bubbles can disrupt the stable functioning of mechanical systems, such as causing unstable operation, loss of control in movements, varnish formation and sticking on valve cores, and corrosion in hydraulic systems.
When there is an increase of foam in the fuel tank, how should it be handled?
Use a clean, dry sampling bottle to collect some oil from the drain port, and observe whether there is water in the discharged oil—free water, or if the oil appears cloudy, stratified, or emulsified and whitish. If water is present, the foam is likely caused by water ingress in the lubricating oil.
If not caused by moisture, check for air leaks and oil level. If everything is normal, take an oil sample for fluid analysis to detect contamination by other chemicals or oils, additive depletion, or oil degradation.
If the fuel tank design is poor, consider increasing the tank volume, installing baffles and screens in the return oil and suction oil zones.
Nairun kindly reminds you: To ensure excellent mechanical lubrication, it is essential to prevent any other substances and oils from entering the lubricant. The oil should be clean, dry, and free from contamination by any other materials.