The hazards and causes of bubbles in lubricating oil

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Those who have worked in the field of equipment lubrication for many years understand the necessity of keeping lubricants clean and ensuring proper pollution control. Lubricating oil must not only be protected from contamination by moisture, solid impurities, particles, etc., but it also needs to be free of air bubbles – whether they are on the surface of the oil or contained within it. The reasons for air getting mixed into lubricant are complex; sometimes it isn’t necessarily a problem with the oil itself. Therefore, adding antifoam agents or changing the oil does not resolve the underlying issue. Let’s take a look at the invisible threat in lubricants – bubbles. First, let’s find out what harms bubbles and foam can cause to lubricants and machinery. 1. Accelerating oxidation and deterioration: Bubbles speed up the oxidation and deterioration of lubricants, accelerate the consumption of additives, impair heat dissipation, prevent the formation of a proper oil film, and thus cause wear on the equipment. 2. Causes localized high temperatures: Bubbles can also lead to localized high temperatures in high-pressure systems, causing the oil to deteriorate rapidly. Furthermore, air is easily compressible; when there are gases in the lubricating oil, the thickness of the oil film decreases or even the oil film breaks down, leading to direct friction between mechanical components and resulting in wear. 3. Erosion damage is caused: Bubbles burst under pressure, which can also result in erosion damage to the metal surface. In addition, bubbles can also cause unstable operation of the equipment. Regarding the issue of bubbles in lubricating oil, oil analysis experts and lubricant technicians have conducted a series of studies. Let’s take a look at what causes bubbles to form: 1. Pure oil does not produce foam on its own; the addition of other substances can cause foaming, such as foreign impurities or additives. Lubricating oils are formulated using base oils and additives. The base oil is the oil as it is, without any additives added; at this stage it is pure and does not produce foam. However, to enhance the properties of the oil, certain additives must be added, such as anti-wear agents, extreme pressure agents, detergents, and dispersants. The more polar additives used, the more likely foam will be generated; for example, both anti-wear agents and extreme pressure agents are polar additives. 2. The size of the bubbles in the oil is related to the surface tension of the oil; lower tension results in smaller bubbles. The smaller the bubbles, the easier it is for the oil to form more stable foam, which is less likely to break apart and disappear. 3. The presence of water in lubricating oil reduces its interfacial tension, making it easier for foam to form. For most oils, even a water content of 1000 ppm is sufficient to cause continuous foam formation. 4. The higher the viscosity of the lubricating oil and the smaller the bubbles contained in it, the slower the bubbles will be released, which results in more bubbles remaining in the oil. It is easy to understand that the larger the bubble volume, the shorter the time it takes for the bubble to rise to the surface of the oil; larger bubbles are more likely to float to the surface. 5. The volume of bubbles is inversely proportional to the viscosity of the lubricating oil; oils with low viscosity tend to produce large bubbles, while oils with high viscosity produce small bubbles. The larger the bubble, the easier it is for it to burst; small bubbles, on the other hand, are relatively more resilient and not easy to burst, so they remain stable after forming and take longer to disappear.