O-ring is a common sealing component. What factors affect its performance? For this issue, the following editor will provide a detailed introduction.
1. Hardness
The hardness of the seal is an important indicator for evaluating its sealing performance. Generally speaking, hardness determines the compression amount and the allowable gap range for groove extrusion. Due to the fact that most of the seals are produced using nitrile rubber, which has a hardness of Shore A70, the seals produced from it can meet most usage conditions. Therefore, if there is no special specification for the material, Shore A70 nitrile rubber is generally used.
2. Squeezing gap
The allowable extrusion gap and system pressure of the seal are affected by the cross-sectional diameter and material hardness. Generally speaking, the higher the working pressure, the smaller the allowable extrusion gap value. Once the gap exceeds the allowable range during use, it is easy to cause the sealing ring to extrude or even be damaged.
3. Compression deformation
Compression deformation is also another important indicator for evaluating sealing performance, where compression deformation mainly refers to the material. Under pressure, the seal will be affected by elasticity and undergo elastic deformation, but generally speaking, it will return to normal after the pressure is removed. However, as the pressure increases, the sealing ring will also deform.
4. Pre compression shrinkage
Generally speaking, the sealing ring needs to be installed in the groove. In order to ensure the sealing performance, a suitable initial compression amount should be reserved before installation. The requirements for pre compression shrinkage of cross-sectional diameter vary in different application scenarios. Most of the time, the initial compression reserve in the static sealing state is about 15% -30%, while in the dynamic sealing state, the initial compression reserve is about 9% -25%.
5. Stretching and Compressing
When installing the seal, it is inevitable that it will be stretched or compressed due to its need to be installed in the groove. Once the values of stretching and compression exceed the standard range, it will cause the cross-section of the seal to decrease or increase excessively. According to actual experimental data, stretching 1% will result in a reduction of about 0.5% in the cross-sectional diameter.
For hole seals, it is necessary to ensure that they are in a stretched state, but the allowable stretching amount is 6%. For shaft seals, they should be compressed along their circumference, and the allowable circumferential compression amount is 3%.
6. Used as a rotating shaft seal
Sometimes, seals can also serve as rotating shaft seals for low-speed rotational motion and short operating cycles. If the circumferential velocity is less than 0.5m/s, it can be designed according to ordinary standards. However, if the circumferential velocity is greater than 0.5m/s, it is necessary to consider the problem of thermal shrinkage of the seal after installation. Therefore, in this case, the inner diameter of the seal ring should be larger, 2% larger than the standard type. After the seal ring is installed in the groove, due to the influence of radial compression, there will be trace ripples in the seal ring in the groove, which will help improve lubrication conditions.
It can be known that the performance of O-rings is affected by factors such as hardness, extrusion clearance, compression deformation, pre compression amount, tension and compression. Therefore, when selecting, attention should be paid to whether various performance parameters meet the standards.
