The O-ring rubber seal has a simple structure and can provide reliable sealing. Therefor O-Rings are widely used in the sealing structure for various vacuum equipments.
In order to get reliable and long life seals in vacuum sealing applications, we have to use the suitable sealing material, well designed and quality controlled O-rings.
Choosing the right vacuum sealing rubber material is crucial.
The selection of rubber material including hardness needs to be based on the following application conditions:
1) working temperature range
2) vacuum pressure
3) media or environment in contact
Fluoroelastomer (FKM/FPM/Viton®) rubber is the first recommended material for high vacuum sealing.
Fluoroelastomer has the following performance characteristics:
1) Application: High temperature, high vacuum, and harsh chemical environments (such as semiconductor industry, aerospace applications)
2) Excellent high temperature resistance: The working temperature range can reach -20 ° C to 200 ° C, and some special formulations can even withstand 250 ° C.
3) Low gas permeability: The extremely low gas permeability reduces leakage in high vacuum environments, ensuring stable sealing performance.
The gas permeability of rubber is mainly determined by the molecular structure of the material. Fluororubber FKM belongs to polar rubber due to strong intermolecular attraction and low gas permeability. At the same time, the molecular chain structure and crosslinking degree of fluororubber are relatively high, which also helps to achieve lower gas permeability.
4) Excellent chemical resistance: It has good resistance to various chemical media such as acids, bases, and solvents, making it suitable for applications in harsh chemical environments.
5) Vacuum Weight Loss.
Some rubber compounds contain small quantities of oil or other ingredients that become volatile under high vacuum conditions and deposit as a thin film on all the surrounding surfaces. Below Table indicates the weight loss of several compounds due to vacuum exposure. Where sensitive surface are involved, the higher weight loss compounds should be avoided.
In some vacuum application scenarios that require high cleanliness, it is necessary to prioritize the selection of low-quality lost rubber materials.
Besides Fluoroelastomer (FKM/FPM/Viton®) material, there are other material could be considered for different working enviroment.
| Material | Working Temperature Range (°C) | Gas Permeability | Chemical Resistance | Wear Resistance | Suitable for High Vacuum |
| EPDM | -40 to 150 | Low | Good | Moderate | Yes (for medium/low vacuum) |
| VMQ | -60 to 200 | High | Good | Moderate | No |
| FFKM | -20 to 300 | Very Low | Exceptional | Moderate | Yes |
| FVMQ | -60 to 200 | Low | Good | Moderate | Yes (for medium vacuum) |
Choose the right compression set for the design of High Vacuum O-ring
Here is the condition as shown in above picture when o-ring assembled. Squeezing occurs with the upper and lower flanges, resulting in radial compression displacement and contact stress between the contact surfaces. When the contact stress exceeds the medium pressure, it will prevent fluid flow to the other side, thus achieving sealing. Therefore, the magnitude of the contact stress reflects the sealing ability of the O-ring, and the necessary condition for ensuring effective sealing of the O-ring is that the maximum contact pressure on the sealing interface is greater than or equal to the medium pressure.
As the compression rate of the O-ring increases, the contact stress and contact width continue to increase.
This indicates that increasing the compression rate of the O-ring is beneficial for enhancing the sealing effect, but too high a compression rate can cause significant residual deformation of the O-ring, stress relaxation, seal failure, and leakage.
Therefore, while ensuring effective sealing, it is important to choose the appropriate compression amount to extend the life of the sealing ring.
In vacuum applications, sealing is mainly ensured by the initial compression load of the O-ring. So we suggest that a larger compression rate can be designed in order to minize the leakage rate.
The influence of surface roughness on the leakage rate of O-ring
The O-RING is mainly sealed by squeezing the contact surface between rubber material and other materials such as steel, as shown in below. The concave part of the flange surface that has not been invaded by rubber will form a leakage channel.
As the roughness of the flange surface increases, the leakage rate also increases. As the increasesing of roughness, the concave part of the flange surface which has not been invaded by rubber will become larger. And then the leakage channel will become larger. Therefore, a smaller machining roughness on the flange surface will help reduce the leakage of the O-ring.
Please contact us, OBT Rubber Seal, for better understanding your technical requirement and our proposal for well quality controlled high-vacuum O-rings.
