Why does hydraulic oil age and deteriorate? How to confirm the best oil change period?

First, the aging mechanism of hydraulic oil
Once the hydraulic oil is produced, it will deteriorate. When the hydraulic system is added, the speed of deterioration will be greatly accelerated, and the performance will gradually decrease until it can no longer be used. Hydraulic oil is classified according to the manufacturing method and can be classified into mineral oil type hydraulic oil, water based hydraulic oil, and synthetic hydraulic oil. Among them, mineral oil type hydraulic oil accounts for more than 90%, so this article only discusses mineral oil type hydraulic oil. The composition of the hydraulic oil base oil is mainly carbon and hydrogen compounds - hydrocarbons, accounting for 96% to 99.5%, and the balance being sulfur, nitrogen and ash.


After the refining of the hydraulic oil crude oil, additives such as anti-oxidation, anti-wear, anti-rust, defoaming, extreme pressure, and pour point depressing are added as needed to prepare the hydraulic oil required for production. When hydraulic oil is used, due to external factors such as air, moisture, impurities, heat, light, mechanical agitation, and internal factors such as the chemical composition of the hydraulic oil and the nature of the additive, physical and chemical changes are required to make the hydraulic oil The overall performance has changed. The causes, influencing factors and results of aging deterioration are shown in Table 5-10.

Deterioration of hydraulic oil can cause equipment wear and the amount of wear (the amount of metal particles in the oil) increases with time. It can be seen from the wear curve of the hydraulic equipment in Figure 3-5 that the wear amount of the E point is slowly increased before the E point. After the E point, the wear amount increases sharply. This indicates that the hydraulic oil has deteriorated and must be changed, so the E point corresponds. Time T (month) and metal content 9 (mg) are the time and indicators of oil change. The rust resistance and corrosion resistance of hydraulic oils decrease with the increase of the use time. If it is reduced to a certain extent, it is necessary to change the oil. Otherwise the hydraulic components will corrode or even break.

Second, how to confirm the best oil change period?
How to choose the best oil change period for hydraulic equipment is an important issue. There are three ways to determine the oil change period: 1 regular oil change; 2 according to the experience and observation of the oil sample to determine whether to change the oil; 3 specified oil change indicators, according to the test results of the oil sample, according to the quality of oil change.


At present, China's factories generally implement regular oil changes. Practice has proved that the regular oil change is out of the quality change of the hydraulic oil during use, and the actual working conditions of the hydraulic equipment are not taken into account. Therefore, it is unscientific not to waste oil due to frequent oil changes, or to cause equipment failure due to the continued use of aging deteriorated oil. The second method is to regularly draw oil in the fuel tank for visual inspection or for simple analysis. This method has certain advantages, but after all, it lacks scientific data.


The third method is the most reasonable and scientific, which can ensure that the hydraulic equipment will not malfunction, damage, shorten the service life due to the hydraulic oil, and can make the hydraulic oil fully and reasonably utilized to prevent waste. . However, this method requires factories and mines to establish laboratories. In the absence of a laboratory, the other two methods are preferred. The following is a discussion of how to choose these three oil change periods.

Third, the development of equipment cleaning and oil change time should consider the following factors:
1. Ambient temperature and pollutants If there is much dust in the environment, high humidity and high temperature, it will promote oxidation or degrade the oil, increasing the viscosity, residue and acidic substances of the oil, causing corrosion to the equipment. At this time, the cycle of equipment cleaning and oil change is shorter.

2. Materials of workpieces processed by the equipment The same equipment is used to process workpieces of different materials, and the cleaning and oil change intervals are different. For example, the frequent oil processing of cast iron workpieces is shorter than that of ordinary metal materials, because the cast iron powder under cutting tends to contaminate the oil, and the catalytic oil deteriorates.


3, the sealing of the equipment The poor sealing, airborne pollutants, processed metal fragments and emulsions easily invade the system, accelerate the wear and tear of the equipment, and the oil change cycle is short.


4, equipment operation time Pipeline or three shifts, long running time, cleaning and oil change time is short. If the single shift or the usage rate is not high, the cleaning and oil change interval is long.

5. Fuel tank filling The cleaning and oil change period of the ground equipment depends on the amount of fuel injected by the fuel tank. Because the oil injection amount is less, the hydraulic oil circulation speed is higher, the residence time in the fuel tank is short, and the heat dissipation condition is poor. Warm high.


6. New equipment or overhaul equipment has a certain roughness due to the friction surface of the new machined surface and new parts. The actual contact area is small, the pressure per unit contact area is large, and the wear speed and wear amount are large during the period of starting operation. Therefore, the cleaning and oil change should be carried out within 3 months after the operation, and then the oil change should be cleaned according to the normal regulations.


7. Oil quality The oil quality is good, the service life is long, and the cleaning and oil change period is long. The hydraulic oil replacement time period is generally 9 to 12 months.