In addition to general physical and chemical properties, each lubricating oil should also have special physical and chemical properties that characterize its use characteristics. The higher the quality requirements, or the more specialized oil, the more prominent its special physical and chemical properties. The test methods reflecting these special physical and chemical properties are briefly introduced as follows:
- (1) Oxidation stability Oxidation stability shows the anti-aging performance of lubricating oil. Some industrial lubricating oils with long service life have this index requirement, so it has become a special performance required by these types of oil products. There are many methods for determining the oxidation stability of oil products. Basically, a certain amount of oil products are oxidized at a certain temperature for a certain period of time in the presence of air (or oxygen) and metal catalysts, and then the acid value and viscosity of the oil products are determined. changes and the formation of sediments. All lubricating oils have different tendency to auto-oxidize according to their chemical composition and different external conditions. Oxidation occurs with the use process, so some aldehydes, ketones, acids, colloids, asphaltenes and other substances are gradually formed.
- (2) Thermal stability Thermal stability indicates the high temperature resistance of the oil, that is, the resistance of the lubricating oil to thermal decomposition, that is, the thermal decomposition temperature. Some high-quality anti-wear hydraulic oils, compressor oils, etc. have proposed thermal stability requirements. The thermal stability of oil mainly depends on the composition of the base oil. Many additives with low decomposition temperature often have an adverse effect on the stability of oil; antioxidants can not significantly improve the thermal stability of oil.
- (3) Oiliness and extreme pressure Oiliness means that the polar substances in the lubricating oil form a firm physical and chemical adsorption film on the metal surface of the friction part, so as to play the role of high load resistance and anti-friction and wear resistance, while extreme pressure property is lubricating The polar substance of the oil is decomposed by the tribochemical action of high temperature and high load on the metal surface of the friction part, and the tribochemical reaction occurs with the surface metal to form a soft (or plastic) extreme pressure film with low melting point, thereby Plays the role of impact resistance, high load and high temperature resistance.
- (4) Corrosion and rust Due to the oxidation of oil or the action of additives, steel and other non-ferrous metals are often corroded. The corrosion test is generally to put the copper strip into the oil, put it at 100 ℃ for 3 hours, and then observe the change of copper; while the rust test is to rust the steel surface under the action of water and water vapor. Add 30ml of distilled water or artificial seawater to 300ml of test oil, then place the steel rod in it, stir at 54°C for 24 hours, and then observe whether the steel rod is rusted. Oil products should have anti-metal corrosion and anti-rust effects. In industrial lubricant standards, these two items are usually required to be tested.
- (5) During the operation of anti-foaming lubricating oil, foam is often generated due to the presence of air, especially when the oil contains surface-active additives, it is more likely to generate foam, and the foam is not easy to disappear. The foam generated during the use of lubricating oil will destroy the oil film, cause the friction surface to sinter or increase wear, and promote the oxidation and deterioration of the lubricating oil. Therefore, anti-foaming is an important quality index for lubricating oils.
- (6) Hydrolysis stability The hydrolysis stability characterizes the stability of oil products under the action of water and metals (mainly copper). This indicator fails. Its measurement method is to add a certain amount of water to the test oil, mix and stir the copper sheet at a certain temperature for a certain time, and then measure the acid value of the water layer and the weight loss of the copper sheet.
- (7) Anti-emulsification Industrial lubricating oil is often inevitably mixed with some cooling water in use. If the anti-emulsification of the lubricating oil is not good, it will form an emulsion with the mixed water, so that the water is not easy to circulate from the bottom of the tank. release, which may cause poor lubrication. Therefore, demulsibility is a very important physical and chemical property of industrial lubricating oil. For general oil products, 40ml of test oil and 40ml of distilled water are vigorously stirred at a certain temperature for a certain period of time, and then the time for the separation of the emulsified layer of the oil layer and the water layer into 40373ml is observed; for industrial gear oil, the test oil is mixed with water, at a certain temperature and 6000 rpm Stir for 5 minutes at /min, let stand for 5 hours, and then measure the milliliters of oil, water and emulsified layer.
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