Apply O-ring seal ring The improvement skills in structure and installation include correct selection of groove shape, correct selection of O-ring hardness, and measures to enhance sealing effect.
The sealing function is mainly to prevent the leakage of working medium and foreign matters such as air, dust and water from entering the hydraulic components and hydraulic system. The quality of the sealing device directly affects the working performance of the hydraulic transmission device. When the design and use are poor, a large number of working media leak, and the system efficiency drops significantly. In serious cases, the system pressure can not rise, resulting in various faults that can not work normally.
The seal failure is mainly caused by its structural design and seal damage. As the most commonly used sealing element, the O-ring has certain skills in design and application in addition to some conventional contents. Mastering these skills can ensure the quality and service life of O-ring seals. This paper briefly introduces these skills that are easily ignored by engineers and technicians.
(1) Correct selection of groove shape
When using O-ring seals, the most common choice is rectangular grooves, but some special parts should not use rectangular grooves, such as rotary seals, semi-circular grooves, flange plates and narrow bolt heads, triangular grooves, etc.
(2) Correctly select "ring hardness"
Reasonable selection of sealing clearance and material with higher hardness can also alleviate the phenomenon of squeezing into the clearance and extend the service life of sealing elements.
(3) Measures to enhance sealing effect
1) Pressure compensation groove. High pressure of the sealed liquid or hydraulic shock will cause leakage of the O-ring. During dynamic sealing, if the pressure exceeds 4MPa, oil may leak. After the retaining ring is added, the pressure can be increased. However, the hydraulic impact will make the local instantaneous pressure several times higher than the normal working pressure, which may cause the O-ring to lose its sealing performance. In this case, the groove with pressure compensation function can be used. With this kind of groove, no leakage is allowed under the pressure of 16MPa. The size of the O-ring groove is: the groove width b is 0.2~1mm larger than the line diameter d1 of the O-ring, and the groove bottom diameter D is 0.2~2mm smaller than the inner diameter of the O-ring. The end near the groove bottom is drilled with 2~4 small holes with a diameter of 2~4mm. The single acting hydraulic cylinder can hit one end, and the double acting hydraulic cylinder can hit two ends (Figure 4-1). The fit clearance between the outer diameter of the piston and the cylinder diameter can be enlarged. The larger the cross section diameter of the o-ring is, the larger the clearance is, generally 0.1~0.5mm. The normal contact point of the seal ring is at the outer diameter (point a). The sealing contact point is at point a and one side (point c). With the increase of pressure, the contact is closer and plays the role of pressure compensation. At the same time, there is no greater requirement for the machining dimension tolerance of the piston, and the surface roughness is R6.3~3.2um.
2) The O-ring can be tilted when rotating the seal. When O-ring is used for rotary seal, the linear speed should not be too high, generally 0.3~0.5m/s is appropriate, otherwise oil leakage will occur. Because when o-ring is used for rotary seal, friction heat will be generated at the contact, the temperature will rise continuously, and oil cut will occur at the contact, causing wear and aging. And the rubber in the tensile state shrinks when heated (Joule effect). That is to say, "friction heat, shrinkage, increased clamping force, friction force,..." repeated cycles, which greatly aggravate the aging, cracking and wear of rubber, leading to seal failure. The amount of leakage is related to the speed. Therefore, the inner diameter of the O-ring is generally designed to be equal to or slightly larger than the diameter of the shaft (3-5%). When installing, compress the ring from outside to inside, and design the compression amount of the section to be smaller (about 5%). In addition, try to use heat-resistant materials, and consider the heat dissipation and lubrication of O-ring. In addition, the O-ring can be installed obliquely (Fig. 4-2). With these measures, the pu value (sealing pressure 6 linear speed) can be reached to 5.6MPa * 7.65m/s=42.84MPa. m/s.
Continuously improve the structural design in production practice to improve the application effect. Prolonging the service life can improve the productivity. Because of the severity of the fault caused by the sealing problem to the hydraulic machinery, the majority of engineering and technical personnel have paid full attention to it, but there has been no perfect solution, which needs further research.
