Application of silicone oil in lubricating oil

Silicone oil is also called polysiloxane. Its silicon oxygen bond is very stable, so silicone oil has good thermal stability and oxidation stability. At present, silicone oil used as lubricating oil mainly includes methyl silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil and ethyl silicone oil. Methyl silicone oil is generally used as damping fluid and base oil for special purpose lubricating grease; Ethyl silicone oil is mainly used for precision instrument oil; Methylphenyl silicone oil is often used to make synthetic high-temperature lubricating grease base oil due to its high temperature resistance, low freezing point and good oxidation resistance; Chlorosilicone oil has better lubricity than other silicone oils, so it is often used to prepare base oil for medium load grease.
The lubricating oil in the lubricating oil system usually operates in a forced circulation mode. Some air often enters the system during operation, which will produce foam and bubbles under intense agitation. Larger bubbles can quickly rise to the surface of the oil, while smaller bubbles rise slowly. No matter what form they exist in the oil, they will have a negative impact on the equipment, which may cause the oil pressure of the oil pump not to rise, affecting the oil circulation, damaging the oil film, and causing wear, At the same time, the oil pressure is unstable, affecting the regulation. In serious cases, foam overflows from the top of the oil tank, threatening the unit operation, so the oil must have anti foam performance.
In order to eliminate the foam produced by the working medium when the equipment system works, after long-term observation and research, a variety of defoaming methods have been found, such as physical defoaming method, mechanical defoaming method, chemical defoaming method, etc. Among them, the chemical defoaming method has the best effect and simple method, so it is widely used at home and abroad. In 1943, Shell Development Company and Gulf Research and Development Company found that liquid organic polysiloxane was a very effective antifoam. Now methyl silicone oil is still widely used as anti foaming agent of lubricating oil. The use of methyl silicone oil as antifoaming agent is related to its following properties: ① the surface tension is lower than that of lubricating oil, which promotes the desorption of foaming agent, but the strength of the surface facial mask formed by itself is poor. ② It has a small solubility in lubricating oil, but has a certain lipophilicity. ③ The chemical property is not active, and it is not easy to react with the lubricating oil. ④ Low dosage, good effect, can effectively eliminate foam in lubricating oil even at high temperature. ⑤ Methyl silicone oil has the advantages of low volatility, good viscosity temperature, high flash point, low freezing point, good thermal stability and long service life. The common viscosity of dimethyl silicone oil that plays the role of defoaming in lubricating oil is (25 ℃ kinematic viscosity) 100-100000cs, and the amount used is 5-50mg.
Silicone oil is a liquid polyorganosiloxane, which has excellent high and low temperature resistance, chemical stability, shear resistance, viscosity temperature characteristics and high compressibility. Vibration reduction products based on silicone oil are widely used in electronic and electrical equipment, tall buildings, bridges and weapon platforms.
The viscosity temperature coefficient of silicone oil is lower than that of organic polymers with carbon chain structure, which is mainly due to the large bond angle and bond energy of silicon oxide silicon bond of silicone oil molecular chain, large degree of orientation freedom and good flexibility. Among all kinds of silicone oils, methyl silicone oil has the lowest temperature viscosity coefficient, and its viscosity changes least with temperature. Therefore, it is most suitable as the base oil of damping fluid. With the increase of temperature, the viscosity of methyl silicone oil changes greatly in the low temperature section, while it changes less and less in the high temperature section. Therefore, methyl silicone oil is a damping material suitable for use at higher temperatures. The damping performance of silicone oil based damping fluid is stable in a wide range of temperature and frequency. However, in order to further improve the damping performance of silicone oil, it is often necessary to add a certain amount of filler to increase the viscosity.
In fact, since the molar mass of general methyl silicone oil has a certain distribution, which is polydispersity, it shows that the viscosity temperature coefficient is also related to the distribution of molar mass, and methyl silicone oil with lower viscosity temperature coefficient can be prepared with methyl silicone oil with different viscosity as the base oil of damping fluid. The common viscosity (kinematic viscosity at 25 ℃) of dimethyl silicone oil as damping fluid is 1000-10000cs.