Recently, a customer reported that too much foam appeared in the use of hydraulic oil and it is difficult to eliminate it in a short time. Today, we will introduce the causes of oil foam and the correct solutions, hoping to help you understand the oil foam problem correctly.
Foam characteristics are specifically divided into foam stability and foam tendency. The national standard of hydraulic oil GB11118.1-2011 has specific requirements for this indicator, that is, foam stability/foam tendency values: procedure I (first 24 ℃) ≯ 150ml/0ml, procedure II (93.5 ℃) ≯ 75ml/0ml, procedure III (second 24 ℃) ≯ 150ml/0ml. The new hydraulic oil from the regular manufacturer will pass the strict foam characteristic test before leaving the factory, and can be delivered to customers only after passing the test.
Causes of forming hydraulic oil foam
On the one hand, the hydraulic oil is mechanically agitated during recycling; on the other hand, the air dissolved in the oil is released when the pressure drops. Under normal pressure, the amount of air that can be dissolved in mineral oil accounts for 8% - 11% of its volume. The amount of air dissolved in lubricating oil increases with the increase of pressure. When the pressure is reduced, the excess air is separated from the oil in the form of bubbles to achieve a new balance. Especially when there is too much oil or the oil under high pressure drops sharply, the foaming situation is more serious. In addition, during the startup of the equipment, when the operating temperature is low or there are some polar compounds in the lubricating oil, a stable foam will be generated, and the foam is not easy to break. The excessive foam in the oil will have adverse effects on the oil itself or equipment operation. The air is trapped in the oil, which greatly improves the compressibility of the oil, makes the transmission response slow, reduces the accuracy of the hydraulic system, and leads to the failure of the control system; When compressed under high pressure, it will suddenly expand under low pressure, causing strong mechanical vibration and increased noise; The density of the oil is reduced, the viscosity of the oil is increased, resulting in poor driving of the hydraulic system. When the temperature is below 0 ℃, the starting performance of the hydraulic device becomes worse; The oxidation speed of oil is accelerated, resulting in precipitation, accelerating the corrosion and wear of mechanical system parts, and the service life of oil itself will be shortened; The use efficiency of the equipment is reduced.
Methods to reduce oil foaming Generally, Anti Foam additives are added to the oil products. At present, the widely used anti foam agent is dimethyl silicone oil. Adding anti foam agent to hydraulic oil can not prevent the tendency of foaming of lubricating oil, but can only reduce the stability of foam adsorption film and shorten the time of foam existence. The surface tension of silicone oil is very small. Due to the reduction of surface energy, silicone oil molecules gather at the interface between oil and air, which is easy to break the bubble film. Therefore, the defoaming effect of silicone oil is good. At the same time, the dosage is small, the volatility is low, and the oxidation resistance and high temperature resistance are good. However, silicone oil is insoluble in lubricating oil. The emulsion of silicone oil and lubricating oil is an unstable system, which is easy to delaminate and lose its defoaming effect. Therefore, anti foam additives are generally used after being diluted with kerosene, so that the anti foam agent can be more stable suspended in the hydraulic oil, playing the due defoaming effect.
