Explain in detail the hydraulic fluid causes and solutions in the hydraulic system

The hydraulic system has the advantages of large capacity, quick response, easy control, large output force and large torque. It is widely used in modern equipment, especially in extra large equipment, but the hydraulic system is generally a combination of electromechanical fluid. Various faults come out, and the fault forms are concealed, diverse, and uncertain. It is difficult to detect and judge. The faults of general hydraulic equipment can be divided into three types: electrical fault, mechanical fault and hydraulic fault. Among them, the electrical fault can be solved by measuring the relevant parameters; the mechanical fault is relatively intuitive, so when the hydraulic system is faulty, the electrical and mechanical systems are first checked. If it is normal, the fault is qualitatively into the hydraulic system. This paper mainly introduces the hydraulic system. In the case of hydraulic system failure caused by oil and its corresponding solution.
There are two main reasons for the failure of the hydraulic system due to the oil problem: 1. The hydraulic oil contains bubbles to cause damage to the hydraulic system; 2. The hydraulic oil contains metal impurities that are harmful to the hydraulic system; The situation is analyzed.
1. The oil contained in the hydraulic oil causes damage to the hydraulic system. Generally speaking, the air contained in the oil is called “mixed air”. In the process of production, storage, transportation and work, the hydraulic oil will inevitably be mixed in the oil. There are two main reasons for mixing air: (1) blending into the oil through the suction pipe of the fuel tank and the pump. If the oil level of the fuel tank is too low, the pump suction pipe is half exposed on the oil surface or the flooding depth is very shallow; The oil pipeline leaks; the system return oil pipe outlet is higher than the oil tank oil surface, and the high-speed injection system oil return coil brings air into the oil, and is again brought into the system by the oil pump. (2) Dissolving a certain amount of oil in a saturated state of air flowing through the orifice or the inlet section of the pump. When the absolute pressure drops to the air separation pressure of the oil, the supersaturated air in the oil is precipitated. The accumulation of fine bubbles that would otherwise dissolve in the oil into larger bubbles occurs in the system.
When the oil contains air bubbles, the damage to the system is quite large from the aspects of the economical operation and the quality of the work of the hydraulic system, mainly in the following aspects:
(1) The system is not working properly. In the hydraulic transmission system, the oil is the transmission medium of the power. In the case where there is no air incorporation, the compression ratio is about (5~7)×10-10m3/N, that is, when the pressure is increased by 10MPa, the volume is only compressed. Reduced to 0.625%. Therefore, oil can be considered as a non-compressible fluid in a general hydraulic system regardless of its compressibility. Once the air is mixed into the oil, the compression ratio will increase greatly. The oil itself has a relatively high stiffness or a large volumetric modulus of elasticity (the reciprocal of the compression ratio) is greatly reduced, seriously jeopardizing the reliability of the system. Such as automatic control failure, intermittent movement of the working mechanism, and increased scrap rate of the workpiece. Mechanical and personal accidents can also occur due to malfunction of the device caused by air bubbles.
(2) The oil temperature rises. When the bubble is compressed at the moment of a pump or the like, its temperature rises sharply. If the gas is not dissolved in the oil, the approximate temperature rise of the adiabatic compression is not difficult to calculate. For example, when the bubble of 35 ° C is pressurized to 3.5 MPa, the temperature rise can reach 580 ° C. After the bubble reaches the high temperature, the oil around it will burn, which is the main reason for the sudden rise of the system oil temperature. However, air is difficult to conduct heat. When there are bubbles in the oil, the thermal conductivity is greatly reduced, which seriously affects the cooling effect of the oil. Will have extremely bad consequences: 1, the general oil temperature is below 90 ° C, with good chemical stability, the oil temperature will accelerate the oxidation of oil; 2, the oil after the deterioration of the oil film strength is not enough to withstand the work The pressure of the load and the lubricating property of the oil are degraded, causing the metal surfaces of the hydraulic system components to contact each other, resulting in a sharp increase in friction and accelerating the wear of the parts. 3. The seals of the hydraulic system are made of various chemical compositions. Sealing rings, mats, etc., require good compatibility with oil and proper working oil temperature. When the oil temperature exceeds the normal heat-resistant temperature of the seal, it will accelerate the aging of the seal;
(3) causing the occurrence of cavitation, causing the erosion of the solid wall surface of the hydraulic system components, which is very harmful to the system;
(4) Air bubbles in the oil increase the vibration and noise of the system, and the volumetric efficiency of the pump is reduced.
Second, the hydraulic oil contains metal, solid impurities on the hydraulic system. There are many precision components in the hydraulic system, some of which have damping holes, some have gaps. If the oil contains metal or solid impurities, it will cause straining of the precision parts, card issuance, blockage of the oil passage, etc., which will endanger the safe operation of the hydraulic system. Generally, the way in which metal and solid impurities are mixed into the hydraulic fluid is: the hydraulic oil is unclean; the refueling tool is unclean; the refueling and repair and maintenance are inadvertent; the hydraulic components are desquamate.
Third, the solution (1) When the hydraulic system is refueling: the hydraulic oil must be filtered and filled, and the refueling tool should be clean and reliable. It is not possible to remove the filter at the fuel filler port in order to increase the speed of refueling. Refuelers should use clean gloves and overalls to prevent solid impurities and fiber impurities from falling into the oil.
(2) When the hydraulic system is being serviced: Disassemble the hydraulic oil tank filler cap, filter cover, detection hole, hydraulic oil pipe, etc., so as to avoid dust when the system oil passage is exposed, the disassembly part must be thoroughly cleaned before opening. If the hydraulic fuel tank cap is removed, first remove the dirt around the fuel tank cap, loosen the fuel tank cap, and remove the debris left in the joint (can not be washed with water to prevent water from seeping into the tank). After cleaning, the fuel tank cap can be opened. If you need to use wiping materials and hammers, you should choose a wiping material that does not remove fiber impurities and a special hammer that is attached to the rubber. Hydraulic components and hydraulic hoses should be carefully cleaned and assembled by high-pressure air drying. Use a properly packaged genuine filter element (the inner package is damaged, although the filter element is intact, it may not be clean). Clean the filter at the same time when changing the oil. Before installing the filter element, carefully clean the bottom of the filter case with the wiping material.
(3) Cleaning of hydraulic system: The cleaning oil must use the same hydraulic oil as the system used. The oil temperature is between 45 and 80 °C. Use large flow to remove impurities from the system as much as possible. The hydraulic system should be cleaned more than three times. After each cleaning, the oil is discharged from the system when it is hot. After cleaning, clean the filter, replace the new filter and add new oil.
(4) Select a special hydraulic oil filter that can be used with the hydraulic system used. For example, the multi-function oil purifier can effectively remove harmful components such as moisture, metal, solid impurities and bubbles in the oil, and improve the quality of the hydraulic oil. Restore its performance.