Do you know the sealing characteristics of the rubber o-ring, which is often used?

General structure of O – shaped rubber ring
O-shaped rubber ring is a commonly used seal in our work, the most commonly used in reciprocating motion, the general structure of the O-shaped seal has two kinds of external structure and internal structure. The structure of o-shaped sealing device (including externally mounted type and internally mounted type) is shown in Figure 1. Usually, the outer structure is used for piston sealing to isolate the internal chamber of the hydraulic cylinder, so it is also called internal sealing; The built-in structure is used for the piston rod seal to isolate the sealing of the inner cavity of the hydraulic cylinder and the atmosphere, so it is also called the external seal. Internal seal leakage happened to leakage, leakage rate is too big, can affect the mechanical efficiency, or unable to maintain normal working pressure, and thus affect the mechanical properties, the leakage rate is too high, not only affects the mechanical properties and mechanical efficiency, but also cause serious pollution in the working environment, thus to control the leakage of sealing device is particularlyimportant.

FIG. 1 Structure of O-shaped sealing device

a）Outside the structure      b）Built-in structure

Sealing principle
Rubber o ring used as the basic role of compression seal: when the O ring is installed between the groove and the sealing surface, there is a certain amount of compression, the resulting rebound to be sealed smooth surface and groove bottom surface with initial compression stress, so as to play a pre-tightening or initial sealing role. The pre-sealing effect of o-ring is shown in FIG. 2。

Fig. 2 Pre-sealing effect of O-ring (installation state)

Because of the pre-seal, the O-ring is in close contact with the sealed smooth surface and the bottom surface of the groove, so that when the fluid enters the groove through the gap, it can only act on one side of the O-ring. Under the working condition, the fluid through the gap to one side of the O-ring pressure is further increased, the O-ring pushed to the other side of the groove and squeezed into a D-shaped state, and the pressure is transmitted to the seal contact surface. Therefore, the seal pressure is actually greater than the fluid pressure applied due to the initial interference pressure action. Pressure distribution of contact surface under o-ring working condition is shown in FIG. 3.

FIG. 3 Pressure distribution of contact surface under o-ring working condition (working condition)

The greater the fluid pressure, the greater the deformation of the O-ring, and thus the greater the pressure transferred to the contact surface, the greater the sealing effect. This effect, which is automatically enhanced by fluid pressure, is called self-sealing, and FIG. 3 appropriately reflects the self-sealing effect of an O-ring.