Intrusion of Air on Hydraulic System Improvements

Talk about the influence of invading air on hydraulic system and improvement measures Wang Wenshen Wu Zhangliang He Hongyan (Department of Mechanical Engineering, Henan Mechanical and Electrical College, Xinxiang 453002) The main cause of vibration, noise, and crawling failures after the system, and put forward the correct use and maintenance of hydraulic equipment. method.

With the rapid development of industrial technology, people pay more attention to product quality and environmental protection issues. Hydraulic technology has been widely used in the national economic sector, and the use of hydraulic transmission has become one of the important indicators to measure the level of a country's industrial level.

Therefore, how to reduce the noise and vibration of the hydraulic device, improve the working performance of the hydraulic system and improve the machining accuracy of the hydraulic cutting machine have become the problems to be solved in various countries. The entry of air into the hydraulic system is the most common factor affecting the normal operating performance of the hydraulic system. Therefore, it is necessary to study the causes of failure of the air to the hydraulic system and to explore measures to improve and eliminate such adverse effects.

1 Influence of the hydraulic system entering the air on the hydraulic oil and its consequences 1.1. Compressibility After the air enters the oil, some of it dissolves in the pressure oil, and part of it forms bubbles floating in the pressure oil. Because the air has compressibility, the hydraulic oil has obvious elasticity, commonly known as the hydraulic spring, so the rigidity of the hydraulic transmission is generally lower than that of the mechanical transmission, and it is easy to produce low-speed climbing or the workbench changes with the load.

1. 2 Oxidation stability If the hydraulic oil is in direct contact with the oxygen in the air, it is prone to chemical reactions especially at high temperatures. After the oil is oxidized, acidic compounds, colloidal precipitates and the like can be generated, which can corrode the metal, and can hinder the system from neutralizing the pipeline and the valve port, thereby seriously affecting the working performance of the hydraulic system.

2 Intrusion of air into the hydraulic system produces vibration, noise phenomena and causes and analysis 2. 1 Noise hazard Unfair noise affects the hydraulic system and performance and life, and induces various failures, while giving the surrounding people a sense of discomfort, in the spirit and health Has an adverse effect. Air into the hydraulic system is one of the main sources of noise. Therefore, it is important to study and analyze the reduction and elimination of hydraulic equipment and noise.

2.2 Analysis of Henan Mechanical and first author College: Male, born in March 1969, BA, lecturer in general hydraulic oil at atmospheric pressure and room temperature, usually in the air can absorb approximately 9. The amount of air dissolved in the liquid and the air pressure in contact with the liquid surface are critical. When the pressure is lower than the separation pressure of the air of the oil at the working temperature, the air dissolved in the liquid will be largely separated out to form bubbles. If the pressure is extremely low and the saturation vapor pressure of the oil is reached, the oil vapor and the air are precipitated together in large amounts to form the boiling phenomenon of the oil. With the operation, the bubbles that are mixed in the oil are broken together at the same time, and localized high-frequency high-frequency waves are generated, sometimes reaching as high as 200 MPa or more and accompanied by local high temperatures. This high-frequency hydraulic shock wave, on the one hand, has a destructive effect on the metal surface of the component, resulting in so-called cavitation phenomena such as metal peeling and pitting. On the other hand, it causes pump and other components to generate large pressure fluctuations and stimulates High-frequency noise. The following figure 1 shows the effect of the air content in the oil on the noise. It is easy to see that the air content increases and the noise increases.

3 Causes and Analysis of the Creep Phenomenon Occurring When the Air Invades the Hydraulic System 3.1 Crawling and its hazards Crawling is a phenomenon that often occurs in hydraulic systems. For example, in a metal-cutting machine tool, unfair crawling can affect the machining accuracy and surface roughness of the workpiece, and it also shortens the service life of the mechanism or tool. Air intrusion into the system is the main cause of crawling. Therefore, it is very important that Boer's cause of crawling and the elimination of crawling are important.

3.2 Analysis of Causes The following takes the hydraulic system crawling physical model shown in Fig. 2 as an example to analyze the mechanism of the crawling of actuators in the hydraulic system.

If air is mixed in the hydraulic cylinder, pressure oil from the left chamber is used to start the movement. When it starts to move, it needs to overcome the large static friction between the guide rail and the guide rail of the bed. At this time, the air bubbles in the left chamber are still compressed ( Figure 2a), table does not move. When the pressure pressure of the left chamber increases, the air bubbles are compressed and the volume is reduced. (Fig. 2b) The table begins to move. At the beginning of the movement, the static friction between the table rail and the bed rail suddenly becomes dynamic friction, the force of the nebula decreases, and the pressure in the left chamber reduces the bubble expansion (Fig. 2c). The piston suddenly accelerates, that is, the table Fast forward. Due to the rapid propulsion of the worktable, on the one hand, the bubbles in the oil discharge chamber are suddenly compressed and on the other hand the oil displacement force is increased. As a result, the back pressure, ie, the pressure in the right chamber increases. This means that accompanied by the work bench rushing, on the one hand, the pressure in the left chamber is reduced and on the other hand the pressure in the right chamber is increased. Its comprehensive action causes the worktable to rush forward and is quickly braked. When the pressure in the work chamber of the hydraulic cylinder rises again to the middle to overcome the static friction force, the worktable restarts and suddenly repeats and stops, thus working The station will suddenly stop beating and continue to circulate, that is to say, there will be table and crawling phenomena.

4 System Structure Main Measures for Entering Hydraulic System 4. 1 System Structure Design 1) Appropriately increase the inner diameter of large suction pipe to reduce or avoid pipe bending 2) For double combined vane pump, the correct piping method should be adopted 3) At the pump outlet One-way valve should be installed at the same time, back pressure valve should be installed on the return road. 4) The exhaust plug should be installed at the highest position of the cylinder or pipe. 5) The design precision of the hydraulic components should meet the technical requirements. 6) The oil tank capacity should be appropriate to make the oil There is enough time to separate the bubbles in the tank.

4. 2 installation and maintenance of the equipment 1) The height of the oil pump should be as small as possible (500mm) 2) The hydraulic pressure should not be too high 3) The sealing of the hydraulic components and pipe head is well sealed 4) The proper oil filter is selected , And should always check, clean, avoid blocking 5) In the fuel tank to maintain a certain distance from the high level of the tubing, or to install a partition between the two) 6) hydraulic control valve hole inlet and outlet pressure can not be too large ( 3. 5Mpa 7) The fuel tank must ensure sufficient oil, the right to use is not less than the oil level indicator line. 8) The viscosity of the oil should not be too high, and it should be replaced regularly as required.