In dynamic sealing devices, friction and wear are significant factors influencing O-ring damage. The degree of wear primarily depends on the magnitude of the frictional force. When the liquid pressure is low, the magnitude of the O-ring frictional force depends on its pre-compression. As the working fluid is pressurized, the frictional force increases with increasing working pressure. Below 20 MPa, this relationship is approximately linear. Above 20 MPa, the increase in the contact area between the O-ring and the metal surface gradually slows down with increasing pressure, and the increase in frictional force also slows accordingly.
Under normal circumstances, the service life of an O-ring decreases approximately quadratically with increasing liquid pressure. Increased frictional force generates significant frictional heat between the rotating or reciprocating shaft and the O-ring. Since most O-rings are made of rubber, which has extremely poor thermal conductivity, this frictional heat causes rubber aging, leading to O-ring failure and compromising its sealing performance. Friction also causes surface damage to the O-ring, reducing its compression.
Severe friction can quickly cause surface damage to the O-ring, resulting in loss of its sealing properties. When used for pneumatic reciprocating seals, frictional heat can cause adhesion, further increasing friction. Even at low speeds, frictional resistance in moving seals can contribute to creep, affecting the performance of components and systems. Therefore, friction performance is a crucial characteristic for moving seals.
The coefficient of friction is an evaluation index of frictional characteristics. Synthetic rubber has a relatively high coefficient of friction. Since seals in motion are typically in a mixed lubrication state involving working oil or lubricant, the coefficient of friction is generally below 0.1. The magnitude of friction largely depends on the surface hardness and surface roughness of the sealed component.