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Vacuum application conditions for O-ring
Vacuum application of O-ring
For a long time, butyl rubber has been the preferred material for vacuum applications. Among rubber polymers used for seals, it has one of the lowest gas permeability. In addition, butyl compounds have low gas release or weight loss characteristics, good sealing physical properties, a useful temperature range of -59 ° C to 121 ° C (-75 ° F to 250 ° F), and good moisture resistance, establishing this preferred position. In addition to low permeability, special environmental factors need to be considered, which usually change the recommendations. Service requirements such as high temperature, radiation resistance, and long-term exposure to water or fluid media combinations may require careful study to determine appropriate recommendations.
3.0.1 Vacuum weight loss
In many space and other vacuum applications, it is particularly important to maintain cleanliness of optical and electrical contact surfaces to achieve the desired objectives. Some rubber compounds contain small amounts of oil or other substances
3.0.1 Precautions for vacuum sealing
The gas flow rate from the pressure side to the vacuum side of the elastic seal largely depends on the design of the seal. Compound B0612-70 has been tested in face type O-ring seals, using grooves that provide 15%, 30%, and 50% compression. From the results plotted in Figures 3-8, it can be seen that increasing squeezing significantly reduces the leakage rate. Lubricating the O-ring with high vacuum grease also significantly reduces the leakage of slightly squeezed (15%) rings, but the effect of grease is much smaller at 30% compression. Under 50% compression, the effect of lubricating grease cannot be detected. Several other compounds were tested in this way and the results were similar.
Increasing the compression of the O-ring reduces permeability by increasing the length of the path through which gas must pass (the width of the ring) and reducing the available area for gas entry (the depth of the groove). Increasing compression often forces rubber into any small irregularities on the mating metal surface, thereby preventing leakage around the seal. Vacuum grease helps seal by filling these small pits and grooves, thereby reducing leakage around the ring. At the same time, it can advantageously change surface tension, thereby reducing surface absorption rate
Therefore, it is recommended to use face shaped O-ring grooves as much as possible for static vacuum sealing. In addition to extensively squeezing the O-ring cross-section, silicone grease is also used as the sealing lubricant and surface coating. When radial sealing is required, or when strong squeezing is not possible due to certain other reasons, the use of vacuum grease becomes even more important.
As an example of the advantage of high extrusion, we found that both Gask-O-Seals and Integral Seals can achieve effective vacuum sealing because they have a large amount of built-in extrusion. Gask-O-Seals have additional advantages, such as high groove filling rate and shallow depth, which can reduce the sealing area exposed to vacuum and prevent rubber sealing components from moving and changing due to vibration or pressure. Another advantage of a high limit percentage is that an increase in temperature does not increase the leakage rate as expected under smaller limits.