The cause of foaming of hydraulic oil and its solution!
December 30, 2021
Occasionally, some customers who use hydraulic oil are consulting, why after their hydraulic oil is regularly filtered to purify impurities, moisture and gas, when the water content in the oil does not exceed the standard, there will still be a lot of foam in the hydraulic oil? Is there any way to eliminate this phenomenon, because the foaming of the hydraulic oil seriously affects the performance of the hydraulic oil. According to the analysis of technical personnel, the above phenomenon mainly considers that the chemical additives in the hydraulic oil have been worn away during long-term use, and certain chemical additives need to be supplemented in time to eliminate this phenomenon. We have compiled some reasons and solutions that affect the foaming of hydraulic oil for your reference:
Reasons for the formation of bubbles On the one hand, the hydraulic oil is mechanically agitated during circulating use, and 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 about 8%-11% of its volume. The amount of air dissolved in lubricating oil increases with increasing pressure. The law is generally expressed as follows: Ⅴg=ⅤoР In the formula: Ⅴg——The volume of air dissolved in oil (at atmospheric pressure and 0℃); Ⅴo——The volume of oil; P-air pressure. When the pressure is reduced, the excess air is separated from the oil in the form of bubbles, allowing it to reach a new balance. Especially when the amount of oil is too much, or the oil under high pressure drops sharply, the blistering situation is more serious. In addition, during the startup of the equipment, the operating temperature is low, and the foam is not easy to burst. When certain polar compounds are present in the lubricating oil, the resulting foam is stable. The speed of bubble separation is called air release (abbreviated as gas release). If the oil has poor gas release, the separation of air from the oil will be slow and the retention time in the oil will be long. The air stays in the oil, which greatly improves the compressibility of the oil, slows the transmission response, reduces the accuracy of the hydraulic system, and causes the control system to malfunction; it is compressed under high pressure, and suddenly expands under low pressure, causing mechanical The strong vibration and noise increase; reduce the density of the oil, increase the viscosity of the oil, cause the hydraulic system to drive poorly, below 0 ℃, make the start performance of the hydraulic device worse; accelerate the rate of oil oxidation , Leading to the formation of precipitation, accelerating the corrosion and wear of mechanical system parts, and at the same time the service life of the oil itself will also be shortened; reducing the efficiency of the equipment. In order to avoid the above-mentioned undesirable phenomena, hydraulic oil is required not only to have good anti-foaming properties, but also to have good air release properties.
Ways to reduce oil foaming Generally, anti-foam additives are added to the oil. At present, the widely used Anti-foaming Agent is simethicone. The effect of adding anti-foaming agent to hydraulic oil can not prevent the foaming tendency of lubricating oil, but can only reduce the stability of foam adsorption film and shorten the existence time of foam. The surface tension of silicone oil is very small. Due to the reduction of surface energy, silicone oil molecules gather on the interface between oil and air, which easily breaks the bubble film. Therefore, the defoaming effect of silicone oil is good. At the same time, the amount of silicone oil is small and volatile. Low, good oxidation resistance and high temperature resistance. However, silicone oil is insoluble in lubricating oil. The emulsion of silicone oil and lubricating oil is an unstable system, which is easy to layer and lose its defoaming effect. The defoaming effect of silicone oil and its durability are determined by the degree of dispersion in the lubricating oil. Generally speaking, the defoaming effect of silicone oil particles is smaller than 100μm, and a few microns is relatively stable. In order to improve the dispersion stability of silicone oil, the silicone oil can be formulated into a solution and added dropwise to the lubricating oil under high-speed stirring (3000-6000r/min). It can also be treated with colloid milling to make the particle size of the silicone oil reach 1-3 µm, even Below 0.5µm. Although silicone oil has a good effect on improving the anti-foaming properties of oil products, it also seriously deteriorates the air release performance of oil products. The factors that affect the air release (deflation) of hydraulic oil are as follows: (1) Viscosity and refined depth of Base Oil The air release of the base oil becomes worse as its viscosity increases. The greater the viscosity, the greater the outgassing value; under the same viscosity, the oil with a shallower refined depth has a larger outgassing value than the oil with a deeper refined depth. . Therefore, the base oil of hydraulic oil requires a deep refining depth. (2) Additives So far, the application of any additive has not been found to improve gassing properties, but their influence levels are different. Antioxidants have no effect on the gassing properties of oil products. Silicone oil and certain pour point depressants have a greater impact on gassing properties, especially silicone oil, even with a content of a few fractions of ppm, which will affect gassing properties. (3) Pollution If the acidic rust inhibitor T746 added to the oil is contaminated by a strong alkali substance, a large amount of insoluble soap will be generated due to the interaction. These soap substances enhance the stability of the bubbles and make the gas outgassing of the oil worse. Ways to improve oil gas outgassing: (1) Improve the refining depth of the base oil. Aromatics, nitrogen, sulfur compounds and other components all affect the gassing properties of the oil, and increasing the refining depth of the base oil will remove more components that affect the gassing properties and improve its gassing properties. (2) Reduce pollution. For oils that may come into contact with alkalis, consider not using acidic rust inhibitors, but use neutral or alkaline rust inhibitors. (3) If using silicone oil anti-foaming agent, add as little as possible. (4) Use non-silicon anti-foaming agent. Non-silicone anti-foaming agents have less adverse effects on oil gassing properties than silicone oil anti-foaming agents.
