Analysis of the causes of deteriorating oil quality

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I. Oxidation: Causes: Generally, it is influenced by three factors: temperature, air, and pressure. II. Pollution: According to statistics, about 70% of failures in hydraulic systems are caused by contamination of the hydraulic oil. 1. Type: (1) Solid particle contamination: Hazard: Seizing of valve components ； Increase leakage ； Filter clogging ； Oil oxidation, etc. Practice has shown that solids with a size of 5–15 μm are most likely to cause the valve to stick; particles ranging from 10–30 μm can lead to wear of the power elements. The oil distribution plate in axial piston pumps is most sensitive to solid particles of 10–15 μm, while radial pumps and motors are most sensitive to particles of 15–25 μm. Vane pumps and motors, on the other hand, are most sensitive to solid particles of 20–30 μm. (2) Water pollution: Hazard: Metal corrosion ； Reduce lubrication ； Form ice crystals ； Cavitation occurs ； Oil oxidation, etc. The water absorption saturation of hydraulic oil is generally between 200 and 300 ppm; the higher the temperature, the better its water absorption capacity. (3) Air pollution: Hazard: Slowed movement ； Cavitation occurs ； Oil oxidation, etc. The oil begins to become cloudy when its concentration in the air exceeds 2%. (The maximum is 8%~10%) The amount of air dissolved in hydraulic oil depends on the following factors: the type of hydraulic oil ； Work stress ； Operating temperature. 2. Methods of expressing pollution level: a. Macroscopic overall representation method: weight level in mg/L ； Parts per million by weight, ppm (by weight) ； Parts per million by volume, ppm (volume) ； b. Microscopic dispersion representation: particle concentration at intervals (the number of particles within a certain size range per unit volume of oil) ； Cumulative particle concentration (the number of particles larger than a certain size per unit volume of oil). 3. Pollution testing methods: The quality of hydraulic oil is assessed on-site by visual inspection; the oil quality is determined by dropping it on fine filter paper, and tests related to hydraulic oil are conducted on-site. Regular sampling and testing are carried out in the laboratory. 4. Proper replacement of hydraulic oil (1) Fixed-cycle oil change method: A method in which the hydraulic oil is replaced after it has been used for half a year, one year, or after 1000–2000 hours of operation (for new systems, the oil is changed for the first time after 500 hours, and thereafter every 5000 hours). This method is widely used, but it is not very scientific. (2) On-site inspection oil change method: Determined based on the usage conditions of the oil on site. (3) Comprehensive analysis of the oil change method: Oil samples are taken for experimental analysis to determine this, and this method conforms to the principles of oil change. 5. Measures to prevent pollution: