In the dynamic sealing device, friction and wear are im […]
In the dynamic sealing device, friction and wear are important factors affecting O-ring damage. The degree of wear mainly depends on the magnitude of friction. When the liquid pressure is small, the friction of the O-ring depends on its pre-compression. When the working fluid is under pressure, the frictional force increases with the increase of the working pressure. When the working pressure is less than 20MPa, the relationship is approximately linear. When the pressure is greater than 20MPa, as the pressure increases, the contact area between the O-ring and the metal surface gradually increases, and the friction force increases accordingly. Under normal circumstances, the service life of the O-ring will decrease approximately in a square relationship as the liquid pressure increases.
The increase in friction force generates a lot of frictional heat between the rotating or reciprocating shaft and the O-ring seal. Since most O-rings are made of rubber, the thermal conductivity is extremely poor. Therefore, frictional heat will cause the aging of the rubber, leading to the effectiveness of the O-ring and destroying its sealing performance. Friction can also cause damage to the surface of the O-ring, reducing the amount of compression. Severe friction will quickly damage the surface of the O-ring and lose its seal. When used as a seal for pneumatic reciprocating motion, frictional heat will also cause adhesion, resulting in a further increase in friction. When the motion seal is moving at low speed, frictional resistance is still a factor that causes crawling, which affects the performance of components and systems. Therefore, friction is one of the important properties for sports seals. The friction coefficient is an evaluation index of friction characteristics. The friction coefficient of synthetic rubber is relatively large.
When the seal is in motion, it is usually in a mixed lubrication state with the participation of working oil or lubricant. The friction coefficient is generally below 0.1. The magnitude of friction depends to a large extent on the surface hardness and surface roughness of the sealed part. 7. Joule heating effect The Joule heating effect of rubber materials refers to the phenomenon that the rubber in the stretched state shrinks when exposed to heat. When installing the O-ring, in order to prevent it from moving in the sealing groove, when it is used as a reciprocating seal, it will not be twisted, and it is generally placed in a certain degree of tension. But if this installation method is used for rotary motion, it will produce undesirable results. The O-ring seal, which has been tightly clamped on the rotating shaft, shrinks due to the frictional heat generated by the rotating motion, thereby increasing the clamping force, so that frictional heat is generated → shrinkage → increased clamping force → friction Heat →……, such repeated cycles greatly promote the aging and wear of rubber.
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