The selection and use of O-ring
The O-ring has good sealing performance and the sealing pressure is in the range of 1.33×10-5Pa to 100MPa. Because of its simple structure, reliable performance, low price and easy selection, it is widely used in various dynamic and static seals. occasion.
1, design points
1.1, O-ring size and material hardness selection
1) Size selection principle
The selection principle of the interception diameter d2 of the O-ring. In order to achieve the best sealing effect, the cross-sectional diameter d2 of the O-ring should be selected as large as possible.
In dynamic sealing applications, considering the dimensional tolerance factor, a larger diameter is recommended for the same inner diameter d1. In static sealing applications, it is safer and more reliable to use a larger cutting diameter than a smaller cutting diameter.
2) Material and hardness selection principles
The hardness of the O-ring material depends on the working pressure, the clearance value and the application (moving and static sealing) and the surface finish quality of the sealing components. For standardized applications, the recommended material hardness is Shore A70, while at high pressure (above 20 MPa) or under pulsed pressure conditions, the hardness of the material needs to be increased accordingly.
1.2, the initial compression after the O-ring is installed
The initial amount of compression (pre-compression) of the O-ring in the mounting groove is critical. Depending on the application, the initial compression of the O-ring is recommended as follows:
Static sealing: when the oil pressure is below 30MPa, choose (15~20)%; when the pressure is in the range of 30~60MPa, choose (20~25)%; when the pressure is in the range of 60~100MPa, choose ( 25 to 30)%. Dynamic sealing: when the oil pressure is below 1MPa, choose (5~10)%; when the pressure is in the range of 1~15MPa, choose (10~15)%; when the pressure is in the range of 15~30MPa, choose ( 15 to 20)%.
1.3, stretching and extrusion
O-rings are allowed to have a certain amount of stretching and extrusion when installed, which does not affect the sealing effect. When used in radial hole sealing applications, the O-ring will be stretched when installed, ie d3 > d1. Recommended stretching amount: take (2 ~ 5)%. In the case of radial shaft sealing, the O-ring will be squeezed when installed, ie da>d6. Recommended extrusion: take (1 ~ 3)%.
The formula for calculating the elongation and extrusion of the O-ring is as follows:
Where d1———O-ring inner diameter (mm); da———da=d1+2d2, where d2 is the O-ring cut-off diameter (mm); d3—the radial bottom hole in the radial hole seal ( Mm); d6———the bottom diameter of the groove in the radial shaft seal (mm); δ1—the amount of stretch; δ2—the amount of extrusion.
1.4, the filling rate of the installation trench
The rectangular area commonly used for O-ring mounting grooves should be greater than the O-ring cross-sectional area of approximately 25%.
Thus, when the O-ring contacts the chemical to cause an increase in volume and shrinkage, the mounting groove has sufficient space to accommodate. Similarly, the pressure of the medium acts on the surface of the O-ring to increase the required contact pressure for better sealing.
The calculation method of the installation trench fill rate is:
1.5, the groove of the installation groove
Rectangular mounting grooves are a common form in which the sides can be machined to a slope of 0° to 5°, and if a retaining ring is used, the sides must be vertical.