In dynamic seals, friction and wear are important facto […]
In dynamic seals, friction and wear are important factors in the damage of O-rings. The degree of wear depends mainly on the amount of friction. When the liquid pressure is small, the amount of friction of the O-ring depends on its pre-compression amount. When the working fluid is subjected to pressure, the frictional force increases as the working pressure increases. In the case where the working pressure is less than 20 MPa, it is approximately linear. When the pressure is greater than 20 MPa, as the pressure increases, the contact area between the O-ring and the metal surface increases gradually, and the frictional force increases accordingly. Under normal conditions, the service life of the O-ring will decrease with a square relationship as the liquid pressure increases.
The increase in friction causes a large amount of frictional heat to be generated between the rotating or reciprocating shaft and the O-ring. Since most O-rings are made of rubber, the thermal conductivity is extremely poor. Therefore, the frictional heat causes the rubber to age, causing the O ring to be effective and destroying its sealing performance. Friction can also cause damage to the O-ring surface, reducing the amount of compression. Severe friction can quickly cause damage to the surface of the O-ring and lose its seal. When used for pneumatic reciprocating seals, frictional heat can also cause sticking, resulting in a further increase in friction.
When the sports seal is used at low speeds, the frictional resistance is also a factor that causes creep and affects the performance of the 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 large. Because the seal is in the moving state, it is usually in the mixed lubrication state in which the working oil or lubricant participates, and the friction coefficient is generally below 0.1.
The amount of friction depends to a large extent on the surface hardness and surface roughness of the seal being sealed.