Leakage Cause of Hydraulic System and Its Solution

Hydraulic system, the leakage of product quality, must be considered. Such as hydraulic cylinders, a serious leak will not only pollute the environment around the equipment, but also lead to lower working chamber pressure of the hydraulic cylinder, the hydraulic cylinder CNC Angle Punching Machine can not work properly. To adopt more advanced methods to effectively prevent leakage, the hydraulic system to achieve “zero leakage” is the hydraulic industry over the years has always been the pursuit of the goal. In addition, the accurate analysis of hydraulic system leakage caused by the initial cause, can help us to eliminate the leakage of hydraulic system failure. As a mechanical students, we through the “hydraulic and pneumatic drive” course of study and access to relevant information, combined with their own professional training, engineering training and daily life in the seen and thought, to common leakage problems, analysis of the hydraulic The form and cause of the leakage of the transmission, and puts forward the measures to control the leakage.
Relative to the mechanical transmission, hydraulic transmission is a new technology, originated in 1654 Pascal proposed static pressure transmission principle. It is a kind of transmission form in which the liquid is the working medium and the energy is transmitted by the energy conversion device. Hydraulic transmission can have the following advantages: ① working fluid can be piped to any location; ② the implementation of the arrangement of components from position constraints, with the connection of the tubing can be easily and flexibly arranged transmission; ③ hydraulic drive can be the original motive of the rotary motion ⑤ The load control, the speed control as well as the direction control are easy to realize, also is easy to carry on the centralized control, the remote control and the automatic control; ⑥ the hydraulic transmission is smooth without vibration; ⑦ has the good lubrication Conditions can improve the reliability of hydraulic components and service life; ⑧ hydraulic components conducive to the realization of standardization Angle Steel Punching Machine, serialization and generalization. Therefore, the hydraulic transmission in the various sectors of the national economy has been widely used.
But the hydraulic drive there are some shortcomings: ① the existence of liquid flow resistance loss, oil leakage and mechanical friction, so the efficiency is low; ② the control temperature is higher; ③ due to the work of liquid leakage and compressibility, Hydraulic system, the poor rigidity of the hydraulic system can not guarantee a strict transmission ratio; ④ the use of working liquid maintenance requirements are very strict; ⑤ high cost of hydraulic components; ⑥ hydraulic system failure to determine and deal with the difficult requirements of the technical level of the staff And higher professional knowledge. The leakage of working fluid has been an inevitable problem, and its solution is also one of the focuses of all walks of life.

drilling metal machine

Leakage form
Leakage can be divided into internal and external leakage leakage. External leakage mainly refers to the leakage of hydraulic oil from the system to the environment, resulting in the hydraulic system of hydraulic piping, hydraulic valves, hydraulic cylinders and hydraulic pumps (hydraulic motors) external leakage is due to high and low pressure side of the pressure difference Such as the leakage of oil from the high pressure chamber to the low pressure  custom processing machine chamber in the hydraulic transmission; the leakage from the pressure channel of the directional control valve to the oil return channel, and the like, which causes the hydraulic oil to flow from the high pressure side to the low pressure side inside the system. Leakage of the main forms of leakage, porous leakage, adhesion leakage and power leakage.
Gap leakage
Engineering machinery hydraulic system, there are two main types of leakage, fixed seal (static joint surface) leakage and movement seal (dynamic joint surface) leakage. The sealing part mainly includes the junction of the hydraulic cylinder head and the cylinder. The movement sealing part mainly includes the hydraulic cylinder piston and cylinder inner wall, the piston rod and the cylinder cover guide sleeve. The size of the gap leakage and pressure, gap and other factors.
2. Porous Leakage
Various components of the hydraulic components in the cover, due to the impact of surface roughness between the two surfaces can not be completely in contact with the two surfaces do not contact the micro-depression, the formation of many cross-sectional shapes, sizes of voids, Size and surface roughness. Multi-gap leakage, the liquid flow through the bending of the many gaps in the sealing performance test done, subject to a certain holding time, leakage can be revealed.
3. Adhesive leakage
Viscous liquid and solid arms have a certain adhesion between the two contact, the solid surface adhesion of a thin layer of liquid, if the solid surface film is thick, the oil film will be due to mutual movement and be The sealing ring scraped off to produce adhesion leakage. The basic means for preventing adhesion leakage is to control the thickness of the liquid adhesive layer.
4. Power leakage
On the sealing surface of the rotating shaft, if there is traces of spiral processing, when the shaft rotates, the liquid flows under the action of the rotating force of the rotating shaft along the groove of the spiral mark. If the direction of the spiral marks coincides with the direction of rotation of the shaft drill machine, power leakage occurs due to the “pump oil” effect of the spiral traces. Power leakage is characterized by the shaft speed is higher, the greater the amount of leakage. To prevent power leakage, should be avoided in the sealing surface of the shaft seal ring and the existence of the “pump oil” role in the processing traces or the use of the principle of power leakage, the use of helical traces of pump oil, the leakage pump back to prevent leakage.
The cause of the leak
The causes of hydraulic system leakage are many and complex, this paper mainly from the seal leakage, working oil pollution, component manufacturing and assembly precision tolerance, oil temperature heat and pressure system, such as hydraulic pressure impact analysis.
(1) Seals: In the hydraulic cylinder, a mention of leakage will first consider the seal, because the seal is the most important hydraulic cylinder to prevent leakage of components. It is mainly YX-ring, the combination of seals, U-ring, V-ring, O-ring, grid to lap, such as Manchester closure. Which YX-type ring, the combination of seals, U-ring mainly by the pressure of the oil pressure generated under tension, so that the inner and outer lips open to achieve the seal, the inner and outer lip linear quality requirements are high; V Type ring, O-ring, lattice to the circle, Lancaster letters mainly rely on the amount of compression to seal. The physical and chemical properties of seals and other aspects of the quality of a direct impact on the quality of hydraulic cylinder products. Seal leakage of the main reasons are the following: ① seal quality problems. Seal material is inferior, and the manufacturing process and accuracy are not up to the requirements, as well as mold and trimming defects. ② seal selection unreasonable. The seals selected do not meet the requirements of working pressure, working speed and temperature, or the types of seals used properly. ③ installation of the seal groove design is not properly, the installation gap and the amount of compression selection is unreasonable; spouse pieces Straightening Machines of the processing accuracy and surface roughness does not meet the requirements; installation without protection and damage to the lips or foreign debris mixed; Temperature, humidity improper, by oxygen and ozone erosion and deterioration and so on. ④ bubble in the liquid seal lip, the bubble is compressed to the original size of a fraction. When the air bubbles reach the non-pressure side of the seal, they release energy quickly, damaging the sealing lip. On the other hand, when a gas containing a certain proportion of oil vapor is pressurized to a sufficiently high temperature, it spontaneously ignites and burns or melts the support ring and even locally burns and carbonizes the seal.
(2) oil pollution: including gas pollution, particle pollution, water pollution. ① gas pollution: Atmospheric pressure, hydraulic oil can dissolve about 10% of the air, in the hydraulic system under high pressure in the oil will dissolve more air or gas. Air in the oil to form bubbles, if the hydraulic support in the process of work in a very short period of time, the pressure between the high and low pressure will quickly change the bubble in the high-pressure side of the high-pressure side of the low-pressure side burst, if the hydraulic system components Surface pitting and damage, the hydraulic oil will be high-speed toward the surface of the device to accelerate the surface wear and tear, causing leakage, the cavitation caused by the corrosion effect known as cavitation. ② Particulate pollution: As the test bed is contaminated by particles, the probability of leakage is small, but in practice still exists. During the use of the hydraulic cylinder, the particles produced due to the above reasons are adhered to the sealing member, and some are adhered to the movable surface, scratching the sealing surface of the sealing member, resulting in failure of the sealing member and leakage of the hydraulic cylinder. This failure to remove the burr is not to clean, clean the various components, and then replace the sealing element can be ruled out; more serious and some will “pull cylinder”, the failure to remove more trouble; more serious can lead to cylinder scrapped . ③ water pollution: the working environment due to moisture and other factors, may make the water into the hydraulic system, water and hydraulic oil reaction, the formation of acidic substances and sludge, reduce the hydraulic oil lubrication performance, accelerate component wear, water can cause The valve stem of the control valve sticks, so that the control valve is difficult to operate, scratches seals, resulting in leakage.
(3) component manufacturing assembly precision tolerance: all hydraulic components and sealing components have strict dimensional tolerances, geometric tolerances and other requirements. If the tolerance in the manufacturing process, such as: the cylinder piston radius, seal groove depth or width of the seal ring hole size and size or due to processing problems caused by rounded, itself has burrs or pits, coating off, sealing Pieces will be deformed, scratched, crushed or pressure is not real phenomena such as the loss of its sealing function, will make the parts themselves have congenital leakage points in the assembly process or the use of leakage occurred. System assembly rough, the lack of vibration, vibration isolation measures; system overpressure, did not follow the provisions of the system timely inspection and wearing parts life expired but not timely replacement will cause system leakage.
(4) oil temperature is too high: hydraulic system work, to control the oil temperature, the temperature is too high, will produce the following phenomena: ① In most cases, when the oil temperature often exceeds 60 ℃, the oil viscosity greatly decreased, Not only make the oil film thinning, friction increases, wear intensified, and the ring expansion, aging, failure, resulting in hydraulic system leakage. According to the research shows that the oil temperature is increased by 10 ℃ each seal life will be halved. ② oil temperature increases, the volume expansion, the pressure increases, while the leakage increases with increasing pressure, so that the increase in leakage. ③ oil temperature so that the gap expansion and contraction changes. Generally with different parts of different materials, thermal expansion coefficient of different materials, when the oil temperature increases, the parts with the expansion and contraction due to different changes will make the gap with the change, when the gap becomes larger, resulting in increased leakage.
(5) the impact of the hydraulic system pressure: the hydraulic system due to frequent change in the higher pressure suddenly start the pump or close the valve and the cylinder block action will cause instantaneous peak pressure up to several times the working pressure, and sometimes enough to seal, Piping or other hydraulic components damage caused by leakage.
Control leakage measures
Leakage of the hydraulic system of construction machinery is the result of many aspects of the overall impact of the existing technology and materials, in order to fundamentally eliminate the hydraulic system leakage is very difficult to do. Only from the above factors affecting the hydraulic system leakage, take reasonable measures to minimize leakage of hydraulic systems.
(1) in the design and processing link to fully consider the important steel cutting machine factors affecting the sealing groove design and processing. The American Society of Automotive Engineers (SAE) recommends the following two solutions to prevent oil spills. ①SAE straight thread “O” ring oil port: Seal by “O” ring, connected by the straight thread; ② SAE4 bolt flange: for larger oil port. In addition, the choice of seals is also very important, the sealing surface roughness is usually static seal table Ra3.2 ~ Ra1.6, dynamic sealing surface Ra0.8 ~ Ra0.4. If you do not initially consider the full impact of the factors of leakage, it will bring incalculable future production losses.
(2) in the hydraulic oil pollution control, we should start from the source of pollution, strengthen the control of pollution sources, but also take effective filtering measures and regular oil quality inspection. In order to effectively cut off the external factors (water, dust, particles, etc.) on the hydraulic cylinder pollution, can add some protective measures.
(3) assembly aspects. Hydraulic system assembly, the components should be tested for pressure performance, check the combination of components with or without external leakage phenomenon, if there is leakage, you should take appropriate measures. Only when all components do not leak seepage can be formally installed into the system. Hydraulic components and hydraulic systems in the assembly, it is necessary to strictly clean, deburring, in addition to welding slag, and the necessary anti-corrosion treatment, in strict accordance with the assembly process requirements for assembly, to eliminate the gap caused by assembly distortion and burrs, And corrosion of the gap formed by abrasive.
(4) to reduce the hydraulic impact. ② the need for frequent commutation of the hydraulic system, as far as possible with a damper with the valve; ③ in the control valve in front of the accumulator set up, the system will be closed, Reduce the shock wave propagation distance, thereby slowing the impact of the hydraulic pressure; ④ increase the diameter of the pipeline to minimize the length of the pipe or rubber hose; ⑤ set the safety valve, the system pressure increases, the unloading effect can be reduced pressure shock. (5) the machine in the run-in period is prone to leakage, which is due to some casting, machining and other defects in the assembly debugging difficult to find, but because of the process of vibration, impact, this defect is exposed, it should be Attention to the run-in period of leakage, for early detection and timely treatment.
(6) from the technical point of view, foreign production is equipped with a test seal (rotary seal) leakage of the new sensor oil seal; and spindle integrated friction seal and labyrinth seal advantages of pneumatic seals have also come out; Component + V-type spring can be used for the pressure of 45MPa hydraulic system “Pan Seal” and other types of combination seal popular.

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