Practice has proved that the pollution of the hydraulic oil of the hydraulic machine is the main reason for the failure of the system, and it seriously affects the reliability of the hydraulic system and the life of the components. Due to the contamination of hydraulic oil in hydraulic machines, the actual service life of hydraulic components is often much lower than the design service life. Therefore, the correct use, management and pollution control of hydraulic fluid in hydraulic machines are important means to improve system reliability and extend the service life of components.
1. Types and hazards of pollutants
Pollutants in hydraulic systems refer to solid particles, water, air, chemical substances, microorganisms, and pollution energy contained in the oil. After the hydraulic oil of the hydraulic machine is contaminated, the following adverse consequences will be caused to the system and components.
①Solid particles accelerate the wear of components, block gaps and oil filters, reduce the performance of pumps and valves, and generate noise.
②The intrusion of water accelerates the oxidation of oil, and interacts with additives to produce viscous gum, which will block the filter element.
③The mixing of air reduces the bulk modulus of the oil, causes cavitation, and reduces the lubricity of the oil.
④Solvents and surface active compounds chemical substances corrode metals.
⑤The formation of microorganisms deteriorates oil, reduces lubrication performance, and accelerates component corrosion. It is more harmful to high water-based hydraulic fluids.
In addition, improper heat, electrostatic energy, magnetic field energy, and radioactive energy are often considered to be pollution to the oil. Some of them cause the oil temperature to exceed the specified limit, causing the oil to deteriorate, and some cause fires.
2. Pollution control of hydraulic oil
The reasons for the pollution of hydraulic oil in hydraulic machines are complex. The hydraulic oil in hydraulic machines is constantly producing dirt. Therefore, it is difficult to completely solve the problem of hydraulic oil pollution in hydraulic machines. In order to prolong the life of hydraulic components and ensure the reliable operation of the hydraulic system, it is a more practical way to control the pollution of the hydraulic oil of the hydraulic machine within a certain limit.
In order to reduce the pollution of the hydraulic oil of the hydraulic machine, the following measures are often taken.
①Clean the components and systems to remove the contaminants remaining in the process of processing and assembly. The hydraulic components should be cleaned after the process of processing the tunnel, and strictly cleaned after assembly.
Before the system is assembled, the fuel tank and pipeline must be cleaned. The residue and surface oxides are removed mechanically, and then pickled and phosphated. The system is fully cleaned after assembly. It is best to clean with the oil used when the system is working, not kerosene. Except for the vent of the fuel tank (with dust cover), all must be sealed during washing. When cleaning, increase the flow rate as much as possible, and use hot oil to flush if possible. The viscosity of mechanical oil at 80°C is 1/8 of that at 25°C, so 80°C thermomechanical oil can wash away many dirt that 25°C mechanical oil cannot wash away. The system should be equipped with a high-efficiency oil filter when flushing, and the components should be activated at the same time, and the welds and connections should be hit with a copper hammer.
② Prevent the intrusion of pollutants from outside. The hydraulic oil of the hydraulic machine will be polluted by the environment during the working process. Therefore, an efficient air filter or a sealed oil tank can be installed on the breathing hole of the oil tank to prevent the intrusion of dust, abrasives and cooling materials. The hydraulic oil of the hydraulic press will be contaminated during transportation and storage. The purchased oil must be left for several days and then injected into the system through the oil filter. In addition, the end of the piston rod should be equipped with a dust-proof seal, which should be checked and replaced regularly.
③ Use a suitable filter. This is an important means to control the pollution degree of the hydraulic oil of a hydraulic machine. Filters with different filtration accuracy and different structures should be selected according to the different conditions of the system, and they should be inspected and cleaned regularly.
④Control the temperature of the hydraulic oil of the hydraulic press. Too high working temperature of hydraulic oil in hydraulic press is not good for hydraulic equipment. The hydraulic oil in hydraulic press itself will accelerate oxidation and deterioration, produce various products, and shorten its service life. Generally, the working temperature of the hydraulic system should be controlled below 60℃, and the hydraulic system of the machine tool should be lower.
⑤ Regularly check and replace the hydraulic oil of the hydraulic machine. At regular intervals, the oil in the system is sampled and inspected to analyze whether its pollution degree is still within the allowable use range of the system. If it does not meet the requirements, it must be replaced immediately. The oil should not be replaced when it is dirty enough to cause the system to malfunction. Before replacing the new oil, the entire system must be cleaned once.
